not to be entirely not following the rules or anything:
NS-777
I love mine, honestly wasn't expecting this level of sound quality (or build quality) for the price (about $50 more than the A5's, check newegg), and I've just been blown away
they're not B&W 800 series, but they're easily better than the Mirage OMNI's, cheaper Klipsch RF, Polk Monitor, Bose whatever, and so on that I spent the better part of last summer driving all over creation to audition
Newegg.com - YAMAHA NS777 Single Three-Way/Four-Driver Bass Reflex Speaker
granted, they are large, and require an amplifier, etc
if they've gotta be active monitors, I like Mackie's active monitors (compared to Yamaha, Genelec, M-Audio, etc) but they're probably a tad over $400
Mackie - Studio Monitors
second to those, I'd probably put the Yamaha active monitors (they're a bit bright for some, but it isn't like screeching)
aside from that, you might look for B&W's 600 series bookshelves (used of course) on audiogon or similar, as they're pretty decent sounding as I recall (haven't heard a pair in ages though), theres also Vienna Acoustics' bookshelf offering (forget what its called, check Best Buy) which is very clean sounding, probably costs about $800 though
and I know Klipsch has some new bookshelves out, Icon or something like that (not the Palladiums), that might fight into your price range, been meaning to try a pair out
and finally, Mirage's nanosat line is pretty nice, as long as you're ok with a sub or two in the system as well