Diaper cake...favors such as homemade lotion in pink or blue...mints...diaper wreath...cake or cupcakes
Pinterest has LOADS of ideas! Or just Google! Here are some to get you started.
Here's a great post on a DIY baby shower.
You can get printables on Etsy for any theme. There are decoration printables, games and invitations. I had them printed at Staples.