Best bookshelf monitor under $1000 new or used.

I own a pair of B&W 602 S3 speakers. These can be purchased used for about 600.00 Oddly enough that's what they also cost new. There's a reason. They're a great value and they are a nice bang for the buck. Most other speakers brands devaluate by a third in a matter of months. They sound great (for 600.00) and don't need much power as long as it's quality. I'm told these were the last of their breed to be built in England. Frankly, to me, they sound a lot better than their current replacement in the B&W line-up. I use them as rear surround speakers now but when they were my mains I enjoyed them every day. The good news is that there are loads of great speakers in your price range. My last suggestion is that you buy something that's used and in great condition. Quality well cared for used gear is as good as it is when it's new except that it's already broken and except for the 602's, usually a lot less money.
Good luck. ps If you go this route, stick with the S3 version.
Mike

As far as new "bookshelf monitor" speakers go, I wouldn't buy without at least listening to a pair of NHT Classic Model 3's.

About the only 3-way in this category, and note the aversion to parallel sides to avoid standing waves.

3-ways have advantages in power handling and more uniform dispersion because each driver gets to operate in a more ideal frequency range for its best bandwidth, dynamic range, and dispersion. And in spite of having two crossovers, transparency is evidently not a problem with this speaker.

The Alon Petite was one of my favorite monitors in the under $1000 category too - very open sounding.

Role Audio Kayaks, tiny (8 x 5.5 x 6.5) giant killers.

Definitely Alon Petite, incredible voice, sound stage and image. Beats my SF Concertinos and even my Proac (Flr Std). Just need to tame the highs depending on the gears you use.