Yeah, pretty much every antweight uses 12mm gearbox motors like these:

http://www.robotbits.co.uk/motors-gearb ... od_10.html
These are the ones all my robots use. The HP motors are the best of these type of motors, more power that ones of a similar type.

However, if you are on a budget:
http://www.ebay.co.uk/itm/6V-300RPM-Tor ... 3366bf48bd