Budget?

What amp do you have, how large is your listening room and how loud do you listen to your music? In that price range, the type of music you listen could also play a role. Finally, what are you upgrading from or are you starting from scratch.

Silverline Preludes if you can find them. Last I knew they retailed at $1500 new so should be able to get them for around $1250 or under 1k used. 

Proac Response 2.5 I saw a pair on eBay under $1,000

Well, since you've given us no info about your priorities in sound characteristics, equipment, or room size, all you'll get here is a crap shoot.  I'll submit Silverline Preludes and Monitor Audio Silver 300s as they get pretty much universally good reviews so a teashot straight down the fairway if you're just looking for flat out great sound.  If you can find used Joseph Audio RM22s or RM25s I'm sure you'll be thrilled.  If you provide us with what sound characteristics are most important to you (i.e. Tone, dynamics, soundstage and imaging, pace rhythm and timing, disappearing, etc.) you'll get better recommendations.