I just finished a Nyan Cat cross stitch as well! It was so fun! The pattern I used is from Birdie Stitching (found at http://www.wingtips.org.uk/ along with tons of pokemon patterns!)
What is really awesome is that I used glow in the dark thread for the little stars ^___^
The only thing I'm sad about is I attempted to use thread I had instead of going out to buy new thread just for the pattern and the only problem with that is that the grey is a bit darker than it should have.
Also, if I make another, I will start with dark blue fabric instead of white so that it really looks like he's running through space!
The only change I made to this last picture is I added more glowing stars LOL couldn't stop myself!