I would first look at the charts on www.servocity.com to get a side by side view of the differences between them. Then check Ebay, however there are cheap knock offs from china and most people wont spot it until too late. I once saw a post showing a "Futaba" picture and in the same post in a different view a knock off with the same Futaba sticker. I sent them a note to show them my displeasure.

Search polulu.com I believe I spelled it right have their brand power HD , they are very reasonable but most important is polulu backs them

http://www.pololu.com/catalog/product/1057

Thanks fellas. Appreciate your help. The servo from pololu looks damn impressive - plenty of torque too!

For the price yea its good , may be a good upgrade , and modifying it to spin continuous would mean lots of torque for a bot to scoot around.

How does one modify this (or any) servo for continuous rotation? I've ripped 'em apart to use as radar motors in model boats, but that generally was severe and left no control.

I know there's a "catch" pin or similar on the main gear, but I think there's more to it than that.

Here ya go buddy , you gotta do a couple things , one is removing the stop pin on the output gear. http://www.instructables.com/id/How-to-modify-a-servo-motor-for-continuous-rotatio/

http://www.youtube.com/watch?v=BM_xm7dLSyI&feature=youtube_gdata_player

Ok this should give you a good idea! , if my regular omnibot motors are not as strong as I want I will probably use 4 or 8 of these servos , that would be 4 on eah side and two on each of my wheels , that's 880 oz in torque per side! , total 1720 oz in adding both sides!