Find some local starving artists and see if they have cheap art to sell, some of it can be fantastic.
Buy it a nice hat.
Paint your walls a new and exciting color.
buy new furnishings...blinds,sofa,lamps,paintings etc.
Buy a spruce tree for christmas
go immediately to apartmenttherapy.com and start your obsession... if you don't know where to start and you have a small apartment, look through the "small cool" contest entries from the past
get a monkey
pictures on the walls.