Besides Target, it looks like Radio Shack will also be offering the Google Play gift cards according to an anonymous Shack employee and a leaked promotional flyer. Based on a screenshot of Radio Shack inventory, it would appear that the cards will be available in $10, $25 and $50 denominations. Just the thing to get for your mobile video game playing friend's birthday.
source: AndroidPolice, Phandroid
A leaked promotional flyer shows that the cards will be coming to Radio Shack in three denominations (R)