My 20" Samsung really is a great monitor: I compared different displays in several malls before I chose it (vivid colors, sharp, good price, flawless for 3 years).
My 2008 MacBook wouldn't support more than a 20" screen anyway. If you have a pro laptop, you may hook up a larger one.
I'm planning to get a 27" iMac sometime, but in anycase my next external display will be a Samsung, no doubt about it.