personally I love alter self, all the benefits of change self (only better) and you can fly, dig, swim...etc...just give your self some knowledge in the different types of humanoids (so you can have some justification for knowing about aquatic elves and other humanoid races) one of my favorite is simply turning into a halfling and manipulating your skin color to match the surroundings, black, green, tan, blue, etc... gives great bonuses to hide, all kinds of cool stuff you can do with this spell, want to fly become a winged elf.