The best mod so far that I've seen

[The Gunslinger]

http://www.l4dmaps.com/details.php?file=13118 Any fan of MW2 or just anyone that wants more powerfull sound shots should give this a try. You can actually feel the power of a shotty if ur speakers have good bass, 10x better than original. And not only shotguns but all other guns as well, makes shooting much more enjoyable. You totally feel like a badass with this mod.