I'll throw a few out there.
1. If you could design a car for a manufacturer, let's see what you would design.
2. The artist's dream car, the car he would like to build if money was not an object of concern.
3. Design a car for CARTOONS.
4. Combine some car designs; let's say the year 1962, Dodge, Ford and Pontiac.
5. An original backwards/forwards car design. Which way is it going?
6. The ugliest car on the face of the earth. No fair using Yugo, Avalanche, Chevette, etc.
There are some madly talented guys on this forum and I applaud you all for your skills.