Here are some links to sites that may be of interest to small-bot authors:
Where to go to get started with Robocode.
Lots of information scattered around about reducing codesize and any other topic in Robocode. Also more detailed information on some of the top small bots and persistent rankings. If the link above doesn't work, try this one.
Source of bots of all shapes and sizes. Their forums have plenty of discussion on codesize reduction as well.
The primary tournament in Robocode. This is where to go to see which are the best MiniBots against a broad range of robots (rather than just against robots of similar size). Seems to have gone inactive without warning.
This now inactive competition is what formally started MiniBot development.