Some1 linked you to kenrockwell's site start there.
If you are willing to shell out $1200, pickup the d7000, it's the latest and best non pro series! Most prod use it as a back up to their main camera. Many have suggested the d90, which is an excellent camera keep in mind it's 3-4 years old! Look into the d7000.
If you are serious about a used camera I've seen a d200 for $450 on portlands Craiglist.
Seeing lots of d80 for under $500 with lens.
If you are willing to shell out $1200, pickup the d7000, it's the latest and best non pro series! Most prod use it as a back up to their main camera. Many have suggested the d90, which is an excellent camera keep in mind it's 3-4 years old! Look into the d7000.
If you are serious about a used camera I've seen a d200 for $450 on portlands Craiglist.
Seeing lots of d80 for under $500 with lens.