If you're willing to use a 3rd party driver instead of the official microsoft ones for the xbox 360 controller, you can use XBCD to fix the triggers as it will let you put each one on a separate axis (or even have them register as regular buttons if you want) instead of the single axis used by the official driver.

http://vba-m.com/forum/Forum-xbcd

If you're going to use a keymapper, for the ones mentioned already in this thread, even though you have to pay for it I like Xpadder better because it has a nicer interface.