Best Places to Look For Used Mac-mini?

[visvaldis]

I have a G4 (MDD). Dual core with 1.25 Ghz With only 80 GB memory it works fine, but the power supply is starting to fail. I installed a used power supply months ago and will have to do it again. It's a great machine and I plan to keep it. It runs the XOS 10.5.
What I'd like is a used Mac-mini with Intel. For my purposes 3 GB RAM and 160 GB Memory are sufficient. More is better, but not necessary.
I'd like a model released in mid 2008 as oldest. I was thinking of spending about $500 to $600. I can use the Dell monitor from my G4 and the mouse and keyboard. I guess I'll have to get an external super drive.
I assume all Mac-minis have the usual iLife already installed. Maybe even a more recent OS than Leopard. I don't need Windows or Microsoft office. I will use InDesign, Photoshop, and Illustrator. Playing with Garageband is also fun!
So far, I've only checked on ebay. What other reliable places offer used, but dependable Mac-minis?
I appreciate all help, tips, and advice.