References when applying?

To those of you that applied to several different shcools, how did you handle your letters of reference. Each school requires 2 or 3 references and some require them on their form. Do you ask many people for references? Do you ask the ones that give you a reference to fill out a few letters? I can't see asking one person to fill out a reference letter to each school I apply to. Please let me know how you did it?

Thank You,

Mitch