Postage rates are going up! New rates are effective May 14, 2007. You can read more about it here. Letters under one ounce will require $0.41 postage. Letters between one and two ounces will require $0.58 postage, which is actually a decrease from the current $0.63 rate -- good news for brides!
I guess this means I should write my long-overdue thank-you cards by May 14, so I can still use my superhero stamps. Heh.