OnMyCommandCM (free at http://www.abracode.com/free/cmworkshop/) lets you write your own CMs using shell scripts.

To install:
1. Download and install OMC.
2. Make sure you have the latest "mate" CLI command.
3. Download OnMyCommandCMs from http://macromates.com/svn/Bundles/trunk/Tools/CM/
4. Import the commands using the OMC_Edit tool in the OMC folder.
5. It expects ~/bin/mate to be the binary. If yours is elsewhere, use OMC_Edit to change the paths.

Commands
========

by Eric Hsu <textmate@betterfilecabinet.com>

-Open in TextMate (pop it up on a file or folder)
-New TextMate file here (pop it up on a directory; if you pick a file, it puts a new file in the same directory)

by Frédéric Ballériaux <fredb7@starflam.com>

-New TextMate file here (alt)

(Same as Eric's version, except it creates the file first (with a dialog asking you for a name) then opens it (with open-a instead of mate).
That means:
The language/Syntax-Highlight is selected according to the file extension
If a file with the same name already exists in the directory, it opens it without any change)

-New TextMate file here with Clipboard text (Same as above, but include the text in the Clipboard, if any.)
-Open selected text in TextMate
-Set type and creator to TextMate
-Edit OMC commands in TextMate
-List folder content in TextMate
-List pkg content in TextMate