This one is really sweet for all you customize to the teeth-er’s out there.
Rockbox is a custom opensource OS for handheld media players. It supports a whole buttload of players including most of the older iPods and a bunch of others I’ve never even heard of.
The interface is easy to navigate and easy to customize with different themes and font sizes and such. It even comes with a bunch of neat little side applications and games (oh god, like I need another place I can play Blackjack). There are lots of cool playback options too, like EQ and crossfading.
Overall Rockbox is a pretty sweet package. I had a bit of trouble with it on my Ipod Classic, but that’s understandable considering that version of the Ipod isn’t fully supported yet.
If you’re looking to spice up your personal media player a bit, go check it out!