Surprised PeepOpen hasn't been mentioned yet. I use it exclusively with MacVim on OSX. It is a bit unconventional but works amazingly well: http://peepcode.com/products/peepopen
I've got this, and I find it's better than Command-T, better than Jamis Buck's now-antiquated FuzzyFinder, and even better than Textmate's own command-t functionality!
At this point, basically, if an editor doesn't support PeepOpen, I won't use that editor.
I actually used PeepOpen a lot when I was still on TextMate, but I totally forgot about it after using Command-T for a while. I'll check it out again if I run into any issues. :)
I have struggled for a while to get PeepOpen and MacVim working together. I can run :PeepOpen, and it will switch to the running peepopen application, but it doesn't load up with the project files. I've tried all sorts of .vimrc config settings that the internet has to offer, but none worked.
At this point, basically, if an editor doesn't support PeepOpen, I won't use that editor.