Without knowing what you want to do with, that's a hard question to answer.
For entry level, I'd say any of the 1920 x 1200 models from Asushttp://www.newegg.com/Product/Product.aspx?Item=N82E16824236046http://www.newegg.com/Product/Product.aspx?Item=N82E16824236047
which I have seen a slow as $199 on "special"
Since it's connected to a Mac, I'm guessing graphics or photo retouch might be of interest and for that stuff, and without giving up gaming or other uses which require fast response times, the Dell U2410 is the entry point. The Dell lists for $599 but every 2 or 3 weeks there are specials and I have seen it as low as mid $400's. Watch THG for specials as well as sites like fatwallet and techbargains.