These formulae provide x11 apps.

Just brew tap homebrew/x11 and then brew install <formula>.

If the formula conflicts with one from mxcl/master or another tap, you can brew install homebrew/x11/<formula>.

You can also install via URL:

brew install https://raw.github.com/Homebrew/homebrew-x11/master/<formula>.rb

brew help, man brew, or the Homebrew wiki.