Here's a promotional "blimp" for the relatively new FOX TV show "Fringe," which I saw being led through the crowd at the Major League Baseball All-Star Parade in New York last summer.
This is a great example of a cheap and effective outdoor treatment; this wouldn't have cost very much, and is a million times more noticeable than the standard outdoor poster (as our friend in the foreground is proving).
All you need:
1. a product you'd like to sell or promote
2. a balloon
5. a guy in a pink shirt and tie to lead it around.