Apart from Force.com's internal editor and Force.com IDE / Eclipse, which applications support syntax highlighting for Apex and Visualforce.
I just found a definition file for Vim, but could not find any for other popular editors and writing systems, i.e. Gedit and SublimeText for editing, and Sphinx/Pygments for documenting.
What other syntax highlighting resources do you know? How would I write my own definition? Is there a reference on Force.com?