Blank Rune

Druids, Sorcerers and Paladins can use blank runes to create spell runes. Since Summer Update 2010, it is not necessary to have the blank rune in your hand, you can simply have it in your backpack and then cast the rune spell.
Say sell rune to NPC A Prisoner and he will tell you he is willing to buy this item off you for 50,000 gp. He ends up paying you a mere 10 gp once you go through with the trade, though.