For those buying cheaper tickets on DL (MRRebates- also a referral link) offers you $2.00 for every purchase. They offer a $5 sign-up bonus and they are really good about the rebates posting on their own. With Ebates, I've had problems every other time where I would have contact them for manual credit and that sometimes takes weeks!

You can split a ticket into two one-way separate purchases and and get $4 rebate.

-Kinglobjaw