I bought mine new a while back (~$3000 AUD) from Apple. Just looking at eBay, they seem to go for a touch over $1000 USD at the moment. I figure they're a bit of a bargain at the moment since they're perfectly capable and have just been replaced by the shiny new model. I mainly develop Ruby Rails/Merb apps with TextMate.
Egads, I love textmate. Another reason I want a mac. That and darkroom and a multitude of other apps. :|
I'll poke around ebay and see if I find anything worthwhile.