Every time I think I'm out, they pull me back in. Hot Wheels Unleashed has had so much content added to it that it's probably four or five times the size of the original release at this point, and stuff just keeps coming to make it even more awesome.
Milestone today released the Looney Tunes Expansion, with five new cars perfectly modeled after the beloved characters they are based on (Bugs Bunny, Daffy Duck, Wile E. Coyote, Road Runner, and Marvin the Martian). There is also a complete new environment to race and build tracks in based on classic Looney Tunes locations. And then there's all the usual stuff - new basement customization items, new obstacles, new music and sound effects. It looks awesome. Check out the trailer here:
The Looney Tunes Expansion can be purchased on its own, or as part of Hot Wheels - Pass Vol. 3.