i've always used Koepi's codec packs in the past, because they were highly recommended on some of the boards i was on. A quick google search turned up this pack, which seems to have everything (minus ffshow): http://www.free-codecs.com/download/ACE_Mega_CoDecS_Pack.htm
Since i've reinstalled my box, i've gotten away from packs, since they can be a pain to upgrade specific filters and codecs. i've installed everything from individual installers/files. This can be a pain too, especially when you want to watch something and you're not sure why it's not working. But it's easier to upgrade, and lessens some of the glut on your system.
I really like K-Lite the best from the other codec packs, it seems to play everything I have without a problem, and it's free from the www.free-codecs.com link that Aoi Tsuki provided.