You haven't mentioned information regarding your room treatment. If you've got a half-decent room (4 bass traps or so) I suggest that you go for M-Audio BX5a. I used to have those but later sold them off in exchange of BX8A (sex). The pads that come along with it are pretty thin, but serves the purpose well enough. However, If you've got plenty of bass traps* in your room getting a sub woofer would be pretty much mandatory.
*As Ethan Winer once said, you can never have too much.
+1 to the post above by Ryan as well.