Interesting comments on the Behringers, I haven't heard them. You do know that a couple in the lead development team at Behringer were the original team for "powered" Mackies>!?
I agree with Tom on the A-2's, as I too, have had experience with the A-5's as well as the Mackie MR8's. I bring these up because they, too, are a bit bigger then a smallish monitor that you may be looking for....however, bang for Buck, I wanted to nominate the MR5-MR8 lines from Mackie. Astounding! The 5's, kind of like the A2's are a bit, and I hesitate to say it, bass shy? The Freaks are there, just not the slam. But, to add the bottom octave to any monitor, a sub is a good bet, unless you want to spend the big bucks and allow ample room on your monitoring station.
Also, whether or not you are mixing surround at all...don't know if that is of interest, seeing as though most of the sound editing software allows for 5 and 7.1 steering, the .1 being the sub
The A-2s are an awesome speaker. The MR5's as well. I am not fond at all of the M-Audios. Some of their peripherals are great, speakers, iMO, are not their forte
I will check the Behringers. I have four of the U-Control USB outboard sound cards (that's what I call it anyway, no drivers, $30, one of the truly great finds for my mobile sound gear on Macs!) and they're incredible! I bought two little 4 channel mixers from them, one sounds great, the other a POS....so, hit or miss for me too, with Behringer
The other way to go is with a decent Home theater receiver, as many are dumping great product for nickels, in favor of HDMI gear. Grab a 5.1 receiver and a nice pair of B&W 601/2 series 2 or 3 speakers from ebay. B&W has a new line of bookshelves out, so these are two or three generations old....but, they sound phenomenal. Paradigm also makes great passive speakers, Thiel, Totem, Wilson, Dynaudio....all depending what you want to spend....your choices are limitless if you go with decent outboard amplification. If you have room for it, this is also a great way to be able to plug in other sources to your computer. Vinyl, High end digital (Outboard DACs), FM tuner, etc. I have a Denon 5803 receiver, about 6 years old, weighs almost 90 pounds and sounds spectacular! An amazing receiver. I have almost 4 grand into it, not a scratch, sat in the same place with nothing on top of it for all 6 years. Perfect condition! I put it on Craigslist and I got no emails! I put it up for $999, with an additional 50 dollar bill and I would hook it up for them....not a single hit! I would never sell it for cheaper than that...I think event that price is too low. There are other things I can do with it...>Bedroom, Garage, etc.
Sorry about the rambling, just wanted to make a point of what is available out there in the receiver world for dirt cheap right now. Look at Rotel, NAD, Denon, Pioneer (Elite), even Lexicon (if you have power amps), and Anthem's pre pros. Again, if it doesn't have HDMI right now, it is dirt cheap. Also, with the pre-inputs on these receivers, they are able to take advantage of the new sound codecs, as long as the processing is done inside the decks (Blu_Ray). I think, with the exception of a couple of Denon transports, this is the case for almost all of them. Not all have 5 or 7.1 channel outputs (analog) but many do. In fact, the Denon 5803 I have, like the Denon 5800 both have 2 "8" (7.1) channel inputs! So you can do SACD with one and Blu-Ray with the other

Not trying to sell mine, in fact, at this point I won't, knowing what the market will and won't bear. BUT, if you can locally find one of these gems....someone just trying to unload an "Old" B&K Ref 50 or Lexicon MC-1....buy IT, hook it up to your workstation, enjoy SONIC BLISS!
Jer