Paypal IPN (subscription system) interest check:

[Regs]

I highly recommend aMember with it's vbulletin plugin:

http://www.cgi-central.net/scripts/amember/

Cost should not be an issue here if you are looking for payments anyways... well, within reason

It has many features that I think would be hard to find elsewhere and you do not only have to rely on paypal... many other payment processors can be used and offered as choices to your subscribers.

The coupons feature is invaluable if you are serious about a subsription model in order to produce time-based incentives. With some creative thinking and implementation, you can use the coupons as a type of affiliate tracking system and give your users seperate batches of coupons to use to get more subscribers

There is a free version you can use to test out certain features, though you have to purchase the pro upgrade and the additional plugin for vB for complete automation.

Additional plugins are available for hivemail, listmail, and a couple of other 3rd party scripts.

Anyways, food for thought in your searches

Cheers,

~Regs.