Thanks for the recommendations. The Xbox 360 controller isn't what I'm looking for, but since it's so popular, I'll pick it up. I'm looking for a controller that works with the W3C gamepad API.
It's not nice to force all users to buy Xbox 360 gamepad which works best.
However, Unity3D supports all gamepad that modern browsers don't work.
This gamepad is for me. The game I'm working on has several control options (touch, virtual gamepad, keyboard, physical gamepad). I wouldn't expect anyone to buy a controller just to play a game.