I developed a Sudoku solver a while ago. It has a command line interface, so just input your puzzle as follows and it'll get solved.
Pretty cool, huh?
As I always said, Android development is a bonus to Java developers. I ported my Sudoku solver and made it an Android application. It's called Sudokroll. As the name suggests, you touch a cell and scroll on the screen to assign a number for the cell.
For better look and feel, it's for Android 2.3 Gingerbread and above. Have fun.