MicDroid is a free AutoTune-style app for Android.
According to the developer, it’s similar to the I Am T-Pain app for the iPhone, but not as fully featured.
It’s based on the AutoTalent LADSPA plugin, by Tom Baran.
MicDroid gives you many options to adjust the pitch of you vocal recordings and gives users the ability to save recordings, make ringtones out of them, and even email them to friends.
It’s available on the Android Market for free, although there is a donation version for $2..99 (in case you want to show support to the developer). The app is purely for entertainment purposes and will probably result in lots of laughter (unless you can actually sing).