I have an early 2006 20" iMac (one of the first Intel ones) and it has one of the best displays I've ever seen. I also have a 1st gen unibody Macbook, and the display on that is pretty crappy.
The first gen 20" iMacs were the midgrade model at the time. The 17" iMacs came with the crappy displays because they were the baseline. Not all 20" iMacs had worse LCDs than the 24" but all 24" iMacs have the best LCDs available.
Within reason of course. Most people won't buy a $1200 calibrated NEC or Lacie.
The 2006 (Core Duo as opposed to Core 2 Duo; white plastic case) iMacs still had Matte displays if I remember correctly, I don't think there were 24" versions of those. Today's 20" aluminium iMacs have awful displays.
