BioWare is apparently so happy with how Dragon Age 2 has done that they are offering a free copy of Mass Effect 2 to all current owners and anyone who buys the game between now and April 30th.
Of course, this only applies to legitimate owners and the copy of Mass Effect you will recieve is for the PC only.
This is a pretty awesome deal, so if you're interested and have a copy of the game, head on over to the Mass Effect 2 promotional giveaway page.