Up to 1000 free DL miles

As blogged by Lucky over on one mile at a time, you can get 500 free DL miles for less than 1 minutes of effort, and 1000 free DL miles for less than 5 minutes.

First get 500 free Northwest (NW) miles through NW WorldPerks University. Very simple questions, takes just a few minutes. Sign up for a new account first if you don't already have one. My miles posted instantly.

Then get 500 free Delta (DL) miles by linking your NW WorldPerks account with your DL Skymiles account. You can opt to leave your NW miles in your NW account, transfer some or all of them to your DL account, or transfer some or all of your DL miles to your NW account. Note that once linked you cannot unlink accounts, but about the only reason not to link accounts would be if you have multiple NW accounts (which is against their T&Cs) and only 1 DL account.