I wrote a habit tracking app a few years ago, it's very simplistic and doesn't look nice but I use it every day and it does what I need it to do:

https://play.google.com/store/apps/details?id=com.doboko.hab...

I've recently got a new phone (was on Android 2.3) so I'm going to try and release a new version soon to take advantage of the better UI available in the newer versions of Android, like the action bar. Going to drop the timer as well as it doesn't work properly, clutters the screen up and I never use it.