I'm surprised you didn't find anything, because there are countless ones.
Equalizer APO (with PEACE GUI) is a popular program that can apply EQ system-wide.
But I'd recommend this software:
http://www.foobar2000.org (music player)
http://www.yohng.com/software/foobarvst.html (lets you use VST programs in foobar2000)
http://www.rs-met.com/freebies.html (parametric equalizer)
http://www.hermannseib.com/english/vsthost.htm (apply changes system-wide)
If you only want to use the EQ in a browser rather than a music player, you just need the last two.
It's also a good idea to reduce the gain in the digital domain by at least the amount of your largest boost/cut to avoid distortion. So just adjust one of the volume controls on your computer. foobar2000 lets you adjust it precisely in decibels, but it will be different for other programs or your computer's volume control itself.