The IRS Economic Stimulus Payment Calculator

Stimulus payments will be sent out in the order of the last two digits of the Social Security number used on the tax return. 
Because the IRS will use the Social Security number to determine when checks are mailed, taxpayers may receive their checks at different times than their neighbors or other family members. On a jointly filed return, the first Social Security number listed will determine the mail-out time.
The IRS expects to make about 34 million payments within the first three weeks after the payment schedule begins May 2. With more than 130 million households expected to receive stimulus payments, more than 25 percent of the payments will be made in the first three weeks.
Taxpayers who choose direct deposit on their federal income tax returns can expect to receive their economic stimulus payments between May 2 and May 16 provided their returns were received and processed by April 15, 2008. For taxpayers who did not choose direct deposit on their tax return but whose returns were processed by April 15, the paper checks will be in the mail starting May 16, with the initial mailings completed by around July 11.