OpenX definitely tends to need regular upgrading to avoid exploits. Anything used that much attracts hacker attention. If you use their market, I find they slow pay, but they do eventually pay, if you pay attention to your stats. OpenX is a very robust solution. I used to love AdCycle, but the folks who eventually became DFP hired the guy who created in. Hmm, looks like
AdCycle is free now. If anyone tries the current version, I'd love to hear feedback on how it works in 2012 because it was seriously awesome years ago. It was what SpookyCash used to use for hosted banner rotations.