<A HREF="http://www.biosmods.com" target="_new">Binary's BIOSMOD</A> has some mod'd BIOSes (as the site name implies) but none of them are for recent mobos. On the main page you'll find some links for mod'd Abit BIOSes. If you dig deeper you'll find IWILL BIOS mods and one Epox mod (8K7A+ I think).
You'll also find a couple of programs, modbin and modbin6, which are for mod'ing Award BIOS bin files. I've never tried it. Needless to say, use them at your own risk.
I don't know where you can find BIOS mods for anything else.
<b>99% is great, unless you are talking about system stability</b>