I did a how to video for connecting a PS2 controller to a Nexus 7. It has everything you need to do it. It cost me 6 dollar because I had the old ps2 controller just laying around. I tried it with a ps1 controller but it did not work.
It also works for connecting the controller to your computer.
Link to all the items:
THE MIKI SHOW | PS2 TO NEXUS 7