If you've received a pre-paid debit card with a note that it's your federal stimulus payment, it's legit. The BBB says they've been getting a lot of calls about people reporting alleged bunk cards but the government moved the payments to cards to get the money out faster.
Also, the IRS has noted on their website that the Economic Impact Payment Card will arrive to your mailbox in a plain envelope reading "Money Network Cardholder Services". Here's hoping you won't be knee deep in a dumpster hunting down your money.