Ink Garden (whom I just love) has a great deal on Personalized magnets! You can get 50 magnets for only $2.00 + $4.99 shipping, so only $6.99 total shipped right to your door (reg. 19.99!). These would be so cute for Party invites since they will easily remind people when the party is. They are also good for business, etc.
Just use the code MAGNET2 at checkout.