I recently upgraded/traded in my D80 for a used D7000 body for 150€ - well worth the money. If you were happy with the D80, I'd look at good condition, lowish shutter count (<50k) used D90 (a noticable upgrade and should be available cheap) or something in the D7xxx range (even larger leap forward, the earlier models should be available at an attractive price)
The D90 has the advantage over the D7xxx that all your batteries & charger are compatible with that of the D80.