Rock 'em, sock 'em Robocode!- My favorite, which tells you how to create a robot. An easy-to-understand tutorial for Robocode.

Rock 'em, sock 'em Robocode: Round 2- A more advanced tutorial for more complicated AdvancedRobots

Robocode Repository- A site that is incompletebut yet it includes many links and many robots' jar files which will help you learn coding.

Robocode Fanatics- The first automatic upload and download robots site, now completely redone with forums and polls.

RoboLeague- A league and season manager for Robocode, written in Java!

SnippetBot Tutorial- A very useful site for learners showing how a SnippetBot is constituted.