I'm quite enjoying this clever work of art by Aaron Kuehn for the Los Angeles County Bicycle Coalition. The book in which it appears comes as a free PDF download, which means you can grab the image and blow it up to print at whatever size you want. And, the rest of the book is pretty sweet as well.
You gotta click through to see all its clever details:
I love the valve!
Aaron also offers the piece as a screenprint, so you can't lose.