I had a bit of time to kill last night, so I ended up making a theme for the R4DS. And guess what is the theme of that theme (pun intended or not, it's irrelevant :P)? It's Space Invaders!
It's a little rough around the edges, since I'm a little lazy at editing the theme.ini. So this is how my first masterpiece actually looks like:
I would probably come up with a set of 12, featuring retro games. But in the mean time, here's the theme, available at YouSendIt.com.