The rapid fire modded Xbox 360 controller is the best way I know of to get an edge in Xbox gaming. I'm pretty sure you've already heard of it if you've made it to this web page, but under the slim chance that you came here unaware, I'll explain what it is briefly.
The rapid fire modded xbox 360 controller has an additional microchip, some wire, two added buttons, and some resistors into it in order to add automatic fire functionality. And yes, you can buy them on the Internet; all over the place.
It will help you out in any game where you can benefit from a rapid fire weapon: Call of Duty, Halo, etc. With this mod you'll be able to outgun anyone using an un-modded controller. Period. All you do is hold down the new button/s and aim. The hardest part is merely in obtaining your controller in the first place, and as I already touched on that's not very hard. You just need a couple bucks and the patience to wait a couple days for the thing to come in your mail.
Your new rapid fire controller will work whether you've got a wireless or a "wired" one. It doesn't matter. In the case where you're playing a game that already has automatic weapons then obviously you won't be able to shoot any faster just because you've now got your rapid fire modded Xbox 360 controller. The thing is though, you will get a better aim off while using the game's automatic firing. So even then it's still helping you out.
When you're shopping for this modded controller, I'd caution you against buying one that advertises a bunch of flashing lights and unnecessary new controls. All that stuff is rubbish and serves very little to no practical purpose. You should really be looking for guys who are producing a laser-tight mod that does one thing and one thing only: give you perfect auto fire capabilities. That's it. I don't think flashing lights are going to help you achieve that end - at all.
So there you have it: everything you ever needed or wanted to know about rapid fire 360 controllers. All in one article. I've told you everything you need to know in order to make a solid and smart purchase.