If you don't mind giving up your credit card info to Google, you can get $10 if you signup for Google Checkout. I got $5 (or was it $10?) of Dana Street coffee when I helped user test Google Checkout several months ago, so I'm becoming quite fond of the service ;). I used my $10 to pre-order the Hellboy Animated Sword of Storms from DVD Empire.

I liked Google Checkout slightly better than PayPal. Checkout can forward e-mails from the seller to keep your address private and the overall experience is a bit more polished (shopping cart looks like seller's, the receipts are easier to read).