You could get a bunch of scrapbooking supplies together or go to one of the large stores (sometimes you can have a scraping party there or there are home consultants that can come to you and host the party). Have everyone make a page or two for mom-to-be and then at the end put it all in a nice album as a gift to her! She will have fun making pages with her friends. You could help out by setting up stations with different supplies geared toward: birth, first steps, first words, first bday, etc.. that way she'll have her first year of baby's important milestones already done!
Making it into a game could be fun also: Have a contest for the most creative or silliest or sentimental and vote on the winners. You could award them a mini scrapbook.
The cake could even look like a baby scrapbook...My mom and I make cakes and I can even see it in my head, it would be really cute!
I have had a lot of success and rave reviews with dessert only parties. It's so easy to throw together and makes for a beautiful presentation.
One thing I find to be really helpful when I've thrown showers is to have everyone fill out the envelope that goes with the thank you notes she'll be sending out (I always purchase thank you notes as a gift to the mom). I just put the envelopes out on a table by the front door and have them stop when they first come in and fill it out with their address and then put it in a basket. Once everyone has arrived I pull one out of the basket for the first door prize. I also print off return address labels for the new mom. It makes her job of sending out thank you's so much easier! She has enough to get ready for as it is!
I've got a million more ideas but I don't want the post to be too long. Feel free to contact me if you need more help. Good luck!
S.