It''ll be hard to beat this:
http://www3.towerhobbies.com/cgi-bin...&I=LXPHD4&P=ML
Digital servos are the way to go, its also stronger than the hitec 645, although its made by hitec. If you are a tower hobbies super saver, you get double warranty, so it''d be 2 year warranty on this servo.