A simple app for looking up sunrise and sunset times for a particular date and location. Easy to use and great for planning if your adventures are light or dark dependant.
A tidy interface and just enough information make this app my go-to for checking weather at my current location. Displayed is the temperature, wind direction and speed, chance of rain, and a 4 day forecast.
Find My Friends
Just like Google Latitude, but with a handy feature to share your location with a specific person temporarily. Reduces communication overhead and keeps you in the loop if you get split up during your adventure.
GPS on ski map by Maprika
A must if you need maps off the beaten track. This clever app lets you take a photo of any map (be it a mountain bike trail map, ski resort map, or even a hand-drawn map), and overlay in on google maps to add anchors. Then you can track your GPS location on your custom map. This is great when the maps app doesn't have the detail you need for your adventure.
I use photosynth for quickly snapping panorama shots which a standard camera app can't do the scenery justice. It's quick, and can save the CPU intensive stitching operation for later if required. Output resolution is decent too.