Pay Services
I recommend four services for payment/password management:
Lancelot--run by Validate, this service is the easiest to set up. You can be up and running in minutes. Their stats are very easy to follow. You can even offer your surfer a free trial; if they don't cancel, they get charged after 7 days. I highly recommend Lancelot.
CCBill--this is a good program for managing larger sites and secure access sites. They have 24/7 live technical support. Many very large companies use them, but they also have time for the smaller webmaster.
I-Bill--this service is also quite large. They take 900 phone calls as payment, also. They are kind of a pain to set up, but once up, they are pretty good.
NetBilling--this company processes transactions on your merchant account. They are much less expensive (1.5% plus 15 cents per transaction) but they do not provide customer support. If you've got a merchant account for credit card billing, you might want to consider them.
Note. I used to recommend WEB800/DMR, but I can no longer do that. During the summer of 1999, they had tremendous reporting and transaction problems. Then, in December of 1999, they lost their ability to conduct transactions on VISA cards. All rebillings which were being done by them on VISA's were essentially lost.