I haven't seen a whole lot of "cash for blood" but a lot of free t-shirts as well as the points card type things that Firefreak already mentioned. We have blood drives at work and most times there is a drawing for a free gift basket or something similar. I'm not sure how many new donors it brings in but it's a nice concept.
Each time I give blood they do some basic lab work and send you the results. Total cholesterol, liver enzymes and a few other tests. So, it's kind of a beneficial thing. Give blood, get free bloodwork!
Next blood drive for me, December 18th!
My immediate boss organizes a blood drive each february for office employees. The big man then gives us a the time off to go donate and to the end of the day thereafter.
My FD and most others on the island organize blood drives. We offer free dinner afterwards...not just snacks and juice. Another does a whole bar-b-q for those who donate.