Best monoblock amps for $2000 used

What is the difference between two mono block amps and one dual-mono stereo amp? Many times you can get the dual-mono stereo amp or even an integrated dual mono stereo amp for a better price.
http://www.musicalfidelity.com/products/m6series/m6500i I had heard this one and it is very good, although this model is discontinued.

Several good suggestions made here. I did not realize there were so many good choices for under $2000.
Please let us know wat you decied to purchase.

I bought three used Marantz MA500 monoblocks 125 watts for like $300 each and they work excellent.

One of my favorite mono block pairs at any price is the SST Ampzilla 2000.  I have seen these a few times for $2500 a pair. 

I am using an Odyssey Stratos Extreme with the Jolida Fusion Pre and it is a very good combo IMO. Very meat on the bones almost tubey midrange but fast and great bass. I would think 2 k will get you into some used nice used Odyssey monoblocks.