Don't use Bitcoin by Bitcoin Android. It is unmaintained, it starts crashing and doesn't load anymore, and there is no way to get your bitcoins out. Someone should really get the developer to take it down. I'm emailing him again now.
Use Bitcoin Wallet. It is maintained by the same team that creates the bitcoinj android library. It is the most reliable app.
Use the MtGox mobile app. This is the best way to ensure that you do not lose coins if the app crashes, since your coins are held at mtgox.
Blockchain has a mobile wallet now as well. Looks very promising.
