Loving Backdrop

Backdrop is a freeware app for Mac that hides everything but the app you're working in.  It's different from Finder's 'Hide Others' command in that it also hides the desktop, and replaces it with a single color that you can tweak.  For scatterbrained compulsives like me, it's great.

Combine that with Megazoomer, specially tweaked for TextMate.  By default, Megazoomer expands the current window to fill the screen. I've got a tweaked version that only expands the window vertically, which makes more sense when you're writing something and want to keep the page normal.