I've been looking for something like this for a while, but couldn't manage to find anything, so I whipped something up myself. I really like the sidebar of the new Finder, but since there aren't any separators you can put in, it's hard to have things like sub-categories of the "Places" section, especially if you've got something like a second Applications folder.
Inspired by all the dock separator packs that are floating around, I mocked up a bunch of fake applications with line-drawing characters as their name, gave them a completely transparent icon, and then put those fake apps in the sidebar as separators.
I've gone ahead and packaged up a bunch of separators, and they can be downloaded from my site.

