If you actually have a clunker and it qualifies (18MPG or less combined mileage, registered and insured for a year under the purchaser's name, etc) you only have another 3 days to take advantage of this program. More info here:
http://cars.gov. I doubt any domestic manufacturers are still offering leases, even if they did, leasing a domestic car would not make financial sense because they depreciate like a rock as soon as you drive them off the lot. If you have to have a domestic car and have the 10K in cash your best bet would be 1-2 year old car, something like a Chevy Malibu or another not very exciting but reasonably well acclaimed sedan. If you were planning to finance, then you should look at leasing or financing a new import. Something like the Nissan Versa, Track309 mentioned or similar (Honda Fit or Civic, Toyota Corolla, one of the Hyundais, etc). Whether to lease or finance would be determined by the manufacturer lease support behind a particular model. Currently, a lot of manufacturers offer 0% financing and if you plan to keep the car for a while that would be a better bet than leasing the same model unless there is a cash rebate on the lease. You don't really need to deal with a dealer unless you are buying a new car. Even then, you can try emailing the Internet sales managers at several dealerships with your specs and get them to commit to a price before you set foot in the dealership. For a used car, you should be looking at private sales or maybe at high volume used car dealers who specialize in buying lots of off-lease vehicles at dealer auctions and reselling them at low mark up. Leasing a used car is usually a very bad deal for the consumer. Most new car dealers make a lot more money from their used car sales operations since it's so much harder for a customer to know what the dealer paid for the car. On top of higher mark up on the used cars, the financing is always several percentage points higher. The only time it may make sense to buy a used car from a new car dealer (IMHO), is when buying a pricey German, English or Italian makes that are "manufacturer certified" and you are basically paying a premium for the extended warranty.