[quote name='Cthulhu8u']I think its been said already, but...
PSN cards don't go on sale because of tax being collected online as opposed to the register like XBL and Wii cards. Sony made a choice not to obfuscate the value of their online offerings like what Nintendo and Microsoft do. Since there is a monetary value being exchanged instead of points, its a giftcard. Gift card=no tax, so in essence they can never go on sale, ever.[/QUOTE]
Never say never, although I don't think it'll ever happen. iTunes cards, which are handled in the exact same manner do and have gone on sale (Wal-Mart, London Drugs, and they're perpetually sold for less than face value at Costco).