The government's Cash for Clunkers program is in full swing, and we've heard several accounts of people combining $4,500 credits with cash rebates and going home with economical, efficient compact cars for less than $8,000 out of pocket. But what if practicality is secondary to your desire to have some fun? Well, you'll probably have to spend more money than $8,000 and you'll have to shop carefully. For instance, muscle cars like Mustang and Challenger are under the program's $45,000 price ceiling, but they don't achieve the required EPA combined fuel economy of 22 mpg (Camaro V6 does, though). Conversely, lightweight performers like the BMW Z4, Lotus Elise and Porsche 911 are adequately fuel-efficient, but too costly. So to help you turn clunker credit into driving excitement, we put together a list of the 10 Most Fun Clunker Replacements.