This will probably be in the next official release of TextMate, but until then I’ve been testing out the AS3/Flex bundle that’s in development. Instructions for installation are available here. The only catch was that I had to explicitly set the path to my svn command in the script to ‘/usr/local/bin/svn’.
The bundle itself is nice. It’s good to have more snippets and autocompletion options (especially for stuff like method and variable declarations). The debug menu also can pop open the flashlog.txt file in the console, which is nice for tracing from the browser.