I was browsing for netbook friendly games and came across this gem (already bought it through the Steam digital download service). This is the cheapest price I've seen this at, digital copy or otherwise (currently costs £5.99 to download on Steam)
Basically it's a very addictive rhythm music game, where you navigate a vehicle along a psychedelic track that's generated by your own MP3s. Absolutely brilliant, and has had a lot of praise and glowing reviews.
It's so cheap I just bought myself a hard copy just for the flexibility of being able to install it without being obligated to install Steam too (sometimes space and resources are an issue, especially on a Netbook).
Be nice, this is my first submission! =)
Edit: If you're interested in seeing how the game plays in motion, here's a good video: http://www.youtube.com/watch?v=ssZdViIssaM