When I custom-build my own, this - from the Cartoon Network's new Brave and the Bold series - is the one:
This is one of the coolest Batmobiles ever. I love the way it combines elements of the 1960s TV series with both modern and classic comic book interpretations. Awesome. The show itself... well, I'm not sure how much longer it's gonna hold my attention.
Update 12/12/08: I do give the series a fairly positive review here.