I have been a plasma and blood donor and I worked at Portland Plasma long ago (crappy job, they treat employees like shit, but donating is safe). As long as you are healthy and have no needle phobia it's fine. Do remember that the red cells are mixed with normal saline before being returned. The saline is chilled. Even room temp is about 20 degrees colder than body temp, so be prepared to feel really cold for a bit afterwards. They should have blankets but you need to ask for one. Get some hot tea or something when you're done. It's temporary and won't harm you if you're healthy. Bring a book or an i-pod or radio with headset, please keep it low so only you hear it. Donating takes a while and is pretty boring, really, you just lie there immobilized. You can donate plasma up to twice a week. Blood can only be donated every 8 weeks, since it takes about 8 weeks to restore red blood cells but fluid volume is restored within about 48 hours. Let me know if I can help you with any more information.
I'm a regular donor (I give four times a year). So, I can give more often with plasma? Are there places that will take it for free? I don't need the cash, I just think we all have a responsibility to give blood.
Call the Red Cross. If you want to give plasma and don't need the money, you can always donate it to a good cause.