I agree, this is a good thread.
I'd like to add that if you're motivated enough, you can use an original Xbox controller. On Xbox live I played nearly 8,000 Halo 2 games, and I bought Halo 2 for Vista last week mostly for nostalgia's sake. Here's the process:
1. Acquire/make USB adapter for Xbox controller S (I already had one, fortunately)
2. Bully Windows 7 (or Vista) into accepting XBCD's program
3. Test the buttons in Halo 2, then change the button assignments in XBCD to reflect what Halo 2 interprets. If anyone is curious, I'll look up exactly what the buttons are, but I don't see the need. (Does this mean that Halo 2 thinks the Xbox controller is a 360 controller?)
My question is whether I still get help with aiming. I didn't pay close attention when I played the other day, but in both (lengthy) games I came away with a +1 kill/death spread.