Retirees and other eligible Social Security beneficiaries will receive $250 this month as part of the recently enacted stimulus plan.  All eligible recipients should have their money by the end of May and will arrive in the same manner as current payments (e.g. check or direct deposit).  The government has a website with all the relevant information.

Nearly 55 million Social Security and Supplemental Security Income (SSI) beneficiaries will receive a one-time payment of $250 each. Individuals who were not eligible for Social Security, SSI, Veterans, or Railroad Retirement benefits at any time during the months of November 2008, December 2008, or January 2009 are not eligible for the one-time payment.

The government website has many more details, including answers to frequently asked questions and an informative video.

See:
http://www.socialsecurity.gov/payment/