I've been using, and loving, the M-Audio BX8d2 Studio Monitors. I went to Guitar Center to pick out a good pair of monitors for my studio and these were my second choice behind the ADAM Audio A7XGB. Those were amazing but a little out of my budget at the time. So for around $500 USD I don't think they can be beat (for pro studio monitors). The sound quality is amazing.
Due to a number of factors, currently I only use a mono unit. An old iHome dock. It's actually pretty good all around for the types of music I play (considering everything), but nothing like my real set up I have at home. My iPhone doesn't dock to it sadly since it's an old 30-pin connector, but it works like a champ and doesn't complain.
I use AudioEngine A5+ with a Bowers and Wilkinson 610 subwoofer, with Meridian Explorer USB DAC.
I originally bought the DAC for my Hackintosh, but have moved it to my iMac. Slam, lots a lots slam! The Dynamics and sheer power for such small speakers, though they are rather large for most people's idea of 'computer' speakers.