Say you copy and paste some snippet of code into yours and it's in HTML. Most often, for me, it's script tags. In Textmate, just select the whole thing, press Cmd+Opt+R, and use html2haml as the command. Use "selection" as the input and "replace selection" as the output.

Just like that, beautiful Haml!

Works with Sass as well. Just use css2sass.

Steve