Considering the disproportionately high number of complaints regarding the current 27" iMacs -- and particularly the complaints about the display -- Apple-refurbished 24" iMacs look to be a "good buy" right now.
The 24" iMacs don't use a newfangled LED-backlight for their displays, and don't suffer from the "yellow tinge problem".
If you aren't one of those fanboys who absolutely has-to-have the "newest, latest, greatest", it makes a LOT of sense.
A good place to keep your eye out for 24" refurbs is here:
http://www.refurb.me/
They don't come into stock as frequently as do the 27" models, but they do show up from time to time.
You can click on the model you're interested in (even if not in stock), enter your email address, and then you'll get a notification when they are in stock again.
The 3.06ghz model is one of Apple's best buys, selling at almost 40% below what it sold for new.