I've found a bunch, now I need to figure out which one is worth spending my free time on. (Wikipedia list)
Reading your other questions on ERPs i sympathise with you. However i don't see many companies using open source ERPs. They are too mission critical. Over the past 12 years I have put some open source software into large companies but it has been hard work.
As a suggestion, what about an open source add on for the ERP you are most experienced with? You've probably got a tonne of ideas of how ERP "X" could be made better if it had "Y". This could be a a fancy maintenance planning tool, a financial reporting system, a iPhone app for authorising transactions...
This would probably keep your interest up, open some more interesting opportunities and it wouldn't hurt if you made it open source as it would help a lot of your fellows and increase your real world rep.
Anyway, i'd be very interested to see where you go with this as i have been, and am in a very similar position.