I'm trying out the StandApp at work this week. That's definitely a goal of mine anyway, and I think the app will be a great way to remember to get up and move more!
In reading other 23 Things blogs, I discovered a utility called MyPermissions that scans other apps to see who has access to your info. I check periodically, but this tool makes it easy to check lots of platforms at once.
I also searched for some others on my own and added Converter Plus, an app that converts things like currency and cooking measurements, and also has "calculators for everyday life", like mortgages.