I no longer post as actively here, but have a few build reports/listings of parts used for 15s over here
For basics I would suggest a Wang box (http://www.rrevo.com/product/36gearboxen/) or P60 for drive. If you want to go brushed a RS550 with a botbitz ESC is fairly bullet proof, if you desire brushless I've had luck with the Turnigy Trackstar 1/10 brushless motor, and Turnigy TrackStar 25A 1/18th.
For your weapon motor, it is really dependent on your weapon type, and weight. I'd suggest for that looking at similar weaponed bots to whatever your design is, and using a similar motor to them.