For some reason, there has been very little fuss over the fact that TextMate now offers code completion for Ruby using the rcodetools gem. It is all still in svn, so you have to check it out manually.
Log for r6455
[NEW] The Ruby bundle now includes an rcodetools-backed completion command on option-escape. This command is capable of very accurate completion for any accessible Ruby objects and methods, without needing to see you type it first (as TextMate’s default completion requires).