• Create a folder in ~/Documents called TextMate Projects
• Save your TextMate Project files there (not the projects themselves)
• Change the icon of the folder to what the ~/Sites folder has (makes sense to me since I use TextMate almost entirely for websites)
• Drag to the right side of your Dock
• Right click the folder in the Dock
  • Display as Folder
  • View content as list

Voilà:

Note: you’ll see .tmproj at the end of the project name until the next time you restart your machine or you restart the Dock (killall Dock). Not sure what the deal is with that.