I recently made the switch from IntelliJ to TextMate. So far I'm happy despite losing some features such as local history and Subversion integration. I haven't really found anything in TextMate that I couldn't do in IntelliJ, but I find I'm happier in TextMate so far. I think fighting with IntelliJ to work with Ruby wore on me. I also found IntelliJ was slightly annoyingly slow.
If you haven't already, I suggest giving TextMate a chance.