CAUSTIC 3 available in the Play Store (and the App Store, iOS lovers!)
The third version of what is possibly the best Android music production app has hit the Play Store and it's absolutely fantastic. People call it "Reason for Android" and I tend to agree - there are modular synths, drum machines, PCM synths that load .sf2 files (the best part, for me, since I mainly make acoustic-sounding music).
Check it out HERE
It's also out for iOS! I know that iPhone/iPad users are not as starved for quality music apps as us Android users but it's still a great app and competitive with the best music production apps on iOS IMHO.