My husband is scared of needles, but gives blood. He says it's not as bad he thought it was going to be.
I am not scared of needles but seeing a bag of my own blood on a trolley next to me makes me feel queasy, I'll be honest! It doesn't hurt though, and as others have said the finger prick is the worst bit (which isn't bad at all imho).
The best bit is you get to lay down for 20 minutes (I donate at work!) and get a free cup of squash and some biscuits, which far outweighs the finger prick (oh, and not forgetting it is for a good cause...)