My favorite inexpensive, high quality full HD HDMI monitor is a ViewSonic VX2770SMH-LED 27-Inch SuperClear IPS LED Monitor (Frameless Design, Full HD 1080p, 30M:1 DCR, HDMI/DVI/VGA). This is a no frills monitor with only a tilt adjustment, speakers, and touch controls, but the rMB (or a MBA) sits on the "foot" nicely if you want to use it in clamshell mode.
You can pick one up on Amazon for about $220. There are 5 of these in my family and everyone loves them. We also have an Apple Cinema Display and an Apple Thunderbolt display which have a definite resolution and feature advantage, but from a "work on it all day" point of view I actually prefer the Viewsonic (I haven't got the best eyesight so I have to turn down the resolution on the Apple monitors anyway).