I’ve made a lot of chiptunes on http://www.beepbox.co. It’s such a nice little tool, I love it! Best of all it stores the entire song in the URL so they can be tweeted without any hassle at all.
Most of my songs are here: http://clint.neocities.org/ (click on Music)
A few of my favorites:
RPG Fight (for the game Dream of an Acacia Tree)
It’s Costanza, George Costanza (an EDM style remix of Tom’s Diner because whytf not)