Best small, desktop speakers, $500 or under (new or used)

I own some of the aforementioned gear and have used several setups, including the Audioengine A2+ - and while they may be very sexy to look at, to my ears they were too small to satisfy without a sub (as hickamore is using them, yes, I am sure then it's a different story!), so they are now in my kitchen instead. My current desktop setup is Mac- SMSL Sanskrit 10th MKII - Emotiva A-100 BasX - Totem Rainmakers. Having said this, I also, like several commenters above, have heard the Vanatoo speakers at an Audio Show in NYC last year and was blown away by how big they sounded. It seemed unfathomable that all that room filling sound came out of them, and I am still trying to find an excuse to buy them to experience them at home… This may not apply to you, but certainly anyone starting from scratch without an amp they want to use, I would recommend checking out those Vanatoos - and I don’t even own them, just can’t get that experience out of my head. I recall youtube reviewer Joshua Valour going into more detail why those speakers are his personal favorites for desktop use.

cornwall IV
damn the torpedos

All the love for RS Minimi should make us recall that they were introduced as "everyman's" knockoffs of Visonik's David and the a/d/s/ L200.  You can disagree, but IMO the a/d/s/ L300 series (C,CC,e) were the best expression of the concept...5" 2-way with their "sticky" fabric dome and in the "e" model, a polymer dome.  I have a pair of the "e"s and consider them perfect for desktop use...coherent, not over-bright, nice punchy bottom, great compact size.  The C & CC versions have a bit more "zing" on the top end, which some may prefer.  You can often find any of these on ebay.

Google "Arche Audio FR2" speakers ($300 delivered) and you will find positive online reviews.

DeKay

I have both Vanatoo Zeros and One Encores.  Excellent self powered speakers with built in DACs.  The One Encores work on a desk or stands.  The Zeros are especially good for Desks.  Very adjustable and sound excellent when you turn off the compressors that are on when sent out from the factory to keep people from overloading them with bass heavy music at a dance party.  Easy to turn off.  I met the company owners at Florida Audio Expo a year ago and their demo was pretty amazing for the price of this product.  Highly recommended for your desk!