There is this new cartoon called Ben 10 on the Cartoon Network.  The
show is pretty crap but the theme song is totally sweet, and by
"totally sweet" I mean "totally awesome".  I've been trying to find a
place where I could get a copy of the song (its by Jellyfish).

I'm not sure if it's technically a Jellyfish somg:

http://answers.google.com/answers/threadview?id=436415

Have a good day.

The Ben 10 theme song is by a singer named Moxy. Her site is:

http://moxymusic.com/

Try this it works for me.  You need some type of a sound capturing
device first of all.  It could be a microphone or a program like
"Sound Capture" (which is free!).  Then all you do is go the the
cartoon network website and hit the record buttom(keyboard commands
work best as they don't click like a mouse does).  It then creates a
nice little .MP3 file for you.  It will have a generated number for a
file name but then you can rename it the way that you want after you
have finished.
You are now done enjoy your "Ben 10 Theme"
This method is intended for personal use ONLY!!!!

The official site http://www.ben10.com now has a link to download an
.mp3 of the theme song, so you can just use that now.