I hope this has not been already posted --But Servo City - mostly a robotics site has great deals on gears- limited in varieties and also small link chain- nylon and metal
Roller chain as low as $6.95 a foot for 1/8" rollers!!
Chain is found under Mechanical and a Acc. Gears where it says gears
See them here-http://www.servocity.com/index.html