I found this through Grasping For the Wind's Geek Media Round-up a few days ago. Geek Art Gallery has done a group of Hello Kitty/Science Fiction mash-ups.
Here's their Hello Kitty Hit Girl.
I also like their Tron and Daft Punk mash-ups. Check out their site for more SF related Hello Kitties or, check out the artist, Joseph Senior's, flicker site for even more mash-ups (including Garfield, Darth Vader, and Bat...girl?).