Well there always seem to be new ways, but reading http://millionmilesecrets.com/2013/01/03/airline-miles-expiration/ here are some easy ones and that site has the right links:
Buy something through the United portal. Can be a $1 iTunes gift card.
Use Bcksgr which gives you miles if you like companies on Facebook (free!)
If you have a credit card
Register with Thanks again
If you don’t mind a little spam
Register with e-miles to get spam.

I’m Rich & Co.

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