Hi Elaine,
There are so many themes it becomes hard to choose. The first thing is to look at the mom, does she have a favorite color? A favorite thing? Or do you want to go with more of a "babyish" theme like wagons, or pooh, or ducks, a star is born, or umbrellas. The sky is really the limit. Think about what things you can make yourself, like a diaper cake, and fun games you can come up with. Once you pick a them, everything doesn't have to have that theme, but it should have the same color. The following links have some great themes, you don't necessarily have to buy from these sites, just get ideas and you can get many items for less at dollar stores and walmart. You can get small baby bottles from the dollar store and fill them with candy/chocolate, tie them with lots of curly ribbon and now you have a great party favor. You can go to vistaprint.com and make your own invitations for near nothing.
http://www.partypail.com/
http://www.baby-shower.com/
http://www.babyshowergamesatoz.com/library/babyshowerthemes.html
http://www.beau-coup.com/baby_shower_favors.htm
http://www.babyshowerstuff.com/
I hope this helps, Let me know if I can be of further assistance
Chase
Research Expert
Publicity/Marketing, Published Writer, Business Owner, World Traveler