I recommend honing your HTML / XHTML / CSS skills for one, working on your OOP/patterns knowledge, and really adopting some MASSIVE sized projects - it will likely show you how much your skill really lacks, on grounds that massive projects require much better organization, etc.

Ruby is always an option, of course. Not much for a complement though. Perhaps you should run with some UNIX administration knowledge (bash scripting, general admin), Perl, or database stuff.