We posted a while back about the introduction of tabs into SubEthaEdit. I recently ran across another text editor that offers tabs called ForgEdit, which bills itself as the "programmers text editor for OS X." It seems to be a rather straightforward app with some decent, if not terribly innovative, features, such as customizable key bindings and a file drawer. I don't think it's going to make me give up TextMate, but if you're looking for an editor with tabs it's probably worth a look.
ForgEdit is a free download while in beta, but will be $20 once it's released.