We've been traveling for almost six months now. Being a techie, I've had fun using my gadgets to make our travels as optimal and stress free as possible.
By far the most useful device is my iPhone 4. It's helped us in both obvious and unforeseen ways. These are the apps I've used the most.
Maps
The Maps app is not as useful unless you have a data plan, which we didn't have due to its prohibitive cost. Most cafes around the world provide free wifi (pronounced wee-fee in most places), but that doesn't help much when you're on the street in a new city looking for your hotel.
Luckily Maps has an undocumented feature that's incredibly helpful for data plan-less users: caching. Maps caches the last n number of map tiles and makes them available for offline use. Before arriving at the next city I make sure I lookup our hotel's location, bookmark the spot, and pan and zoom around the map to preload as much as I can. The iPhone's cache is not limitless and I believe the iPhone 4's cache is larger than the iPhone 3G and 3Gs, but this trick works on all models.
As a bonus, GPS and compass both work without an internet connection, so if you've loaded the right tiles you'll have no problem getting around.
OffMaps 2 (link)
Even with the previously mentioned trick, it's good to have a backup. OffMaps 2 utilizes the open source Open Maps and makes them available for offline use. This app does cost money and will nickel-and-dime you for each city you download, but the developers did a nice job with the UI and added other useful features, such as public transportation overlays and store/restaurant/cafe lookup.
Instapaper (link)
I was a huge fan of Instapaper before leaving on the trip and now I'm a bigger fan. Instapaper is a simple service and iPhone app that lets you save articles to read later. Its killer feature is that it syncs your content for offline use, which makes long bus/train/plane trips more tolerable.
The easiest way to get articles into your Instapaper account is with the provided javascript bookmarklet. However, if you're solely relying on your iPhone as your portable computer, a less-used alternative is to email the URL of the article you want to save to your special Instapaper email address, which can be found after you've logged in to the Instapaper website.
Podcaster (link)
Podcasts are another terrific and cost effective way to pass the time on long journeys. The built-in iPod app lets you play podcasts that you've synced with iTunes, but if you don't travel with a laptop or you don't sync often you'll soon find yourself with nothing new to listen to. Podcaster is a paid app that does many things, but most importantly it lets you sync podcasts directly through the app without the need of a computer.
Camera
Duh. Of course you're going to use the camera to take shots of whatever awesomeness is in front of you. But I've found the camera to also be useful as a visual notetaking tool. Need to record the departure schedule from Fes to Chefchouen posted in the bus station? Take a picture of it. Worried about getting lost in a city without street signs? Take shots of unmistakeable landmarks.
Geotag Photos Pro (link)
I'm a little obsessed with geotagging my photos. Unfortunately I take most of my photos with a DSLR, which does not have a built-in GPS. However, the iPhone does and there are plenty of apps that will record your location as you wander through the city. Geotag Photos Pro has worked great for me and is definitely worth the money.
Turn it on at the start of your day and by the end you'll have a geo dataset that you can mash up with your photos using Aperture or other applications. You can also load your dataset into Google Maps and see your superimposed breadcrumb trail directly on an interactive map (ie, this was how we spent one day in Madrid). It makes for a nice digital souvenir.
Also, If you've preloaded the maps within the app (like the Maps app, GPP will cache the last n tiles) you can use your trail to backtrack if you're lost or return to a place you saw the other day and wanted to return to.
Currency (link)
This free app provides a simple and clean way to lookup the current currency conversion rates. The XE app (link) is also good and I carry both on my phone.
Convert Units for Free (link)
Due to our assine insistance of sticking to unit measurements that none of the rest of the world uses, you'll need an easy way to convert a kg, km, or lt into lbs, mis, and ozs. This app has a crappy UI, but it gets the job done.
Skype (link) and Google Voice (link)
Skype is an indispensible service for communicating with friends and family back at home. The iPhone app is better than the PC/Mac version due to its portability.
Before we left Melissa and I ported our cellphone #s to Google Voice. Although the Google Voice iPhone app does not include VOIP for inbound and outbound calling, it does provide a nice interface for checking voicemails and sending/receiving text messages.
Everyday (link)
Everyday is a simple app that facilitates taking a portrait of yourself everyday and turning the collection into a video slideshow. It's more fun than essential. Here's my Everyday video from a few months ago.
By far the most useful device is my iPhone 4. It's helped us in both obvious and unforeseen ways. These are the apps I've used the most.
Maps
The Maps app is not as useful unless you have a data plan, which we didn't have due to its prohibitive cost. Most cafes around the world provide free wifi (pronounced wee-fee in most places), but that doesn't help much when you're on the street in a new city looking for your hotel.
Luckily Maps has an undocumented feature that's incredibly helpful for data plan-less users: caching. Maps caches the last n number of map tiles and makes them available for offline use. Before arriving at the next city I make sure I lookup our hotel's location, bookmark the spot, and pan and zoom around the map to preload as much as I can. The iPhone's cache is not limitless and I believe the iPhone 4's cache is larger than the iPhone 3G and 3Gs, but this trick works on all models.
As a bonus, GPS and compass both work without an internet connection, so if you've loaded the right tiles you'll have no problem getting around.
OffMaps 2 (link)
Even with the previously mentioned trick, it's good to have a backup. OffMaps 2 utilizes the open source Open Maps and makes them available for offline use. This app does cost money and will nickel-and-dime you for each city you download, but the developers did a nice job with the UI and added other useful features, such as public transportation overlays and store/restaurant/cafe lookup.
Instapaper (link)
I was a huge fan of Instapaper before leaving on the trip and now I'm a bigger fan. Instapaper is a simple service and iPhone app that lets you save articles to read later. Its killer feature is that it syncs your content for offline use, which makes long bus/train/plane trips more tolerable.
The easiest way to get articles into your Instapaper account is with the provided javascript bookmarklet. However, if you're solely relying on your iPhone as your portable computer, a less-used alternative is to email the URL of the article you want to save to your special Instapaper email address, which can be found after you've logged in to the Instapaper website.
Podcaster (link)
Podcasts are another terrific and cost effective way to pass the time on long journeys. The built-in iPod app lets you play podcasts that you've synced with iTunes, but if you don't travel with a laptop or you don't sync often you'll soon find yourself with nothing new to listen to. Podcaster is a paid app that does many things, but most importantly it lets you sync podcasts directly through the app without the need of a computer.
Camera
Duh. Of course you're going to use the camera to take shots of whatever awesomeness is in front of you. But I've found the camera to also be useful as a visual notetaking tool. Need to record the departure schedule from Fes to Chefchouen posted in the bus station? Take a picture of it. Worried about getting lost in a city without street signs? Take shots of unmistakeable landmarks.
Geotag Photos Pro (link)
I'm a little obsessed with geotagging my photos. Unfortunately I take most of my photos with a DSLR, which does not have a built-in GPS. However, the iPhone does and there are plenty of apps that will record your location as you wander through the city. Geotag Photos Pro has worked great for me and is definitely worth the money.
Turn it on at the start of your day and by the end you'll have a geo dataset that you can mash up with your photos using Aperture or other applications. You can also load your dataset into Google Maps and see your superimposed breadcrumb trail directly on an interactive map (ie, this was how we spent one day in Madrid). It makes for a nice digital souvenir.
Also, If you've preloaded the maps within the app (like the Maps app, GPP will cache the last n tiles) you can use your trail to backtrack if you're lost or return to a place you saw the other day and wanted to return to.
Currency (link)
This free app provides a simple and clean way to lookup the current currency conversion rates. The XE app (link) is also good and I carry both on my phone.
Convert Units for Free (link)
Due to our assine insistance of sticking to unit measurements that none of the rest of the world uses, you'll need an easy way to convert a kg, km, or lt into lbs, mis, and ozs. This app has a crappy UI, but it gets the job done.
Skype (link) and Google Voice (link)
Skype is an indispensible service for communicating with friends and family back at home. The iPhone app is better than the PC/Mac version due to its portability.
Before we left Melissa and I ported our cellphone #s to Google Voice. Although the Google Voice iPhone app does not include VOIP for inbound and outbound calling, it does provide a nice interface for checking voicemails and sending/receiving text messages.
Everyday (link)
Everyday is a simple app that facilitates taking a portrait of yourself everyday and turning the collection into a video slideshow. It's more fun than essential. Here's my Everyday video from a few months ago.