I unabashedly love TextMate, and I love my TextMate themes. I do, however, spend a fair amount of time in Xcode, which is why I was excited to find XThemes. With a little bit of drag and drop, you can convert any TextMate theme -- in all of its splendor -- into an Xcode theme.
Yes, it's for a limited audience ... namely TextMate die-hards who also use Xcode frequently enough to miss the themes they love (and have probably spent a fair amount of time tweaking). If you fit into this niche, you'll definitely want to take a look. XThemes: $0. Feeling at home coding outside of TextMate ... priceless.