I used to politely say "no thanks" or "I'm not interested". IF they kept up the schtick - which now I can understand why they do, I would say no again and then hang up. After a while I would say no once and then hang up if they kept talking. Now, the minute I realize what type of call it is, I wait to make sure it is not something like MADD, and then just hang up without a word.

"A fanatic is someone who can't change his mind and won't change the subject" Churchill