I feel pretty lost without my iPhone, doubly so when traveling. Here’s some of the iPhone apps I found useful on a recent trip to France. Many of these apps cache data on the phone, both to save on roaming charges and for responsiveness.

MapsWithMe ($0): street maps. Caches vector data from OpenStreetMap and then renders maps on the phone. I used to use OffMaps but their raster tile approach just takes up too much space. With MapsWithMe I could download super-detailed maps for all of France with no sweat.

Navigon ($20 – $100): turn-by-turn driving directions. No need for a standalone GPS, the voice prompting and routing is good enough to drive all over France and Norway. Shop carefully to avoid their random pricing; right now it’s $65 for all of Europe, or $90 for just France. TomTom is a strong competitor. Bring a car charger.

Wiki Offline ($10) and AllOfWiki ($10): cached copies of Wikipedia. Really great for research. The 5GB data dump is text only and has some formatting issues, but it’s usable. Both apps work well and you only need one; I think I slightly prefer the Wiki Offline UI.

Accio French-English ($5): translation dictionary. There’s better language software out there, Accio is cheap and good enough for quick lookups.

Photogene² ($1): photo editing. Photogene makes it easy to crop, correct exposure, and upload. iPhone 4S photo quality is great and I really like uploading photos on the fly during a trip; I’ve been home 3 weeks and still haven’t gotten to the 200 photos on my “real” camera.

Twitter ($0): social networking. Tweets are the Internet’s postcards. Particularly good with photos. I’m still looking for a way to archive all my tweets into a journal; here’s a Storify view of my trip to France.

Traboules ($1): Lyon sightseeing. Only useful if you’re going to be in Lyon, I’m linking it here because it’s remarkable. The tourist office commissioned an augmented reality iPhone app; you look through the iPhone screen to see the world with overlaid markers for the Traboules, a hidden bit of Lyon.