John, it is a good thing you ask. There are servo's that drift, so be
careful. It is normally the "no-name brands". I mostly use JR servos
(both R/C and PIC projects) and I never seen it drift. Other good makes
(but not limited to) are Futaba, FMA, Hitec and Multiplex.

Karlton Spindle of Multiplex ( http://www.multiplexrc.com/ ) can give
you some good advice.
Other you can try:
http://www.jrradios.com/
http//:www.fmadirect.com

Look out as well for a new servo called "digital servo". Got very good
holding power and accuracy.

Quentin