STN - Cheap, uses less power, slow refresh rate
TFT - More expensive, uses more power, high refresh rate, crisp image.
Some STN displays have gotten really, really good (especially those LG's and Samsungs) , and some TFT's aren't so hot, but it's a rule of thumb to which 98% obey.
(i got that off the web from another forum archive, but thought it was good to post)