We're having one. Pinterest does have great ideas. Etsy has good invitations as well. I'm going to do the balloon reveal. We find out the sex March 30th!
We didn't have a party, but for our reveal we made cupcakes. Covered them in icing so you couldn't tell what they were and decorated them with question marks, B ' s, G's and other baby related things. Then we took a picture of all the cupcakes, a picture of me holding a B and my husband holding a G, and then a picture of us holding the cupcakes up to reveal the blue cake.
For a party you could have a cake that you need to slice into to reveal, or a box full of one color balloons, or a scavenger hunt leading to a piece of paper that says girl or boy.