Preacher Curls
Also known as the "Scott Curl", made a mainstay by one of my favorite bodybuilders Larry Scott, this is a pretty straightforward exercise, and also does a great job of hitting those biceps.
To start, set the preacher bench at 80-90 degrees, making sure that the bench is padded enough to comfortably support your arm, nestles under your armpits, and adequately supports your elbows. This part is very important, as you want to focus on your exercise and your biceps, and not thinking about how your skin is being pinched, or how your elbows are being aggrivated by the movement.
Start with arms out straight, and then curl the bar up towards you. As always, perform each rep in a controlled fashion, concentrating on contracting the biceps as you rep. Lower the bar back to the start position. Remember: never "bounce" the weight up. This can cause a torn bicep muscle, torn ligament, and really disrupt your muscle building plans!