Thanks for the suggestions. After reading more posts, I don't think a competition is the way to go. We don't want to set up any bullying or pressure for people who either can't donate or choose not too.
If there's another blood drive, I'm going to just volunteer to send out all the emails with statitics and fun facts about donations - I know I wish that more information about sickle cell anemia had been published considering many clients and employees are African American.
I'm also going to suggest more door prizes and try to arrange for really high end snacks. Food seems to be a good motivator at my office. I'm going to see if we can get the Houston Texans or Astros to donate tickets to use for a door prize.

Or maybe a gift certificate to a coffee shop or nearby deli.
Our regional blood center lets you build up credits for donations towards things like t-shirts, blankets, umbrellas, mugs, etc. You can also donate your points back to the blood center to help cover admin costs or towards a new donor coach. You have to sign up for the Commit For Life program. I may play up that too -
So I think incentives are the way to go.