As with many sweepstakes, you have to be 18 to enter these two cash sweepstakes, so that means I'll be able to in just a few more months.
1) Road & Track Cash Giveaway Sweepstakes
2) Car and Driver Cash Giveaway Sweepstakes
For the sweepstakes from Hearitfirst.com, you can be 13 or older.
3) Hearitfirst Sweepstakes (including an iPod Touch and a Dell Netbook)