I also just noticed they have Gamma World in POD format...
1st edition
www.drivethrurpg.com
3rd edition
www.drivethrurpg.com
4th edition (FASERIP rules)
www.drivethrurpg.com
And most of the 1E/2E/3E/4E modules in POD (Including Gamma Knights and the Overlord of Bonnpar*)
They also have 2nd (the first edition I remember owning), 6th (D20 modern, by WW) and 7th (D&D 4E rules) - but not in POD. I couldn't find the 5th edition (Alternity rules).
* The original Overlord came in a folder packet with 3 minibooks. I'm planning to get a softcover version that's an all-in-one smaller and more durable.