At a recent Slashdot discussion a lot of people mentioned Yamasaki Catleap, it could be shipped from Korea where it's supposedly produced from 27'' panels rejected by Apple, but still usable. And it costs 340-400 USD with shipping.
As for the topic, it's really puzzling how people can use just laptops as their main work machines for code development. Right now I have about 6Mpixels at 100dpi of screen estate and I guess I could make use of another 4Mpixels. Good keyboard is also a must.
http://www.rockpapershotgun.com/2012/02/22/hard-choices-the-...
If you want really cheap, LG has some 23" (1920x1080) IPS panels for right around $200.
I recall it getting good reviews on AnandTech although I can't seem to find the link now.
Have been using mine with a MBA at home, love it.