Donation Cards on tables in honor of your guests in lieu of party favors. Sponsoring a charity on your wedding day is a nice touch, especially if you are personally connected to a charity.
Think Green — to save money on your flowers, try using more greenery than blooms in your church arrangments or garlands on archways, trellises, etc. Ferns and vines are both inexpensive and easy to obtain! Silk flowers are gaining popularity as well.