Mike,
Check out this site for some good and some amusing options:
http://www.ultimatecupholders.com/competitors.html
I especially like the roll of duct tape and the sneaker.
I just went down to Pep Boys and looked around until I found one that would fit between the seats against the rear wall. Put Velcro on the bottom and the back. Sticks great to the carpet, but comes off easily by lifting up on the front when you don't want it. Stores in the trunk when not in use. Nice to have a place to drop change or a cellphone too.
They have tons of things like this at Autozone and Pep Boys.
Cheers!
Dave