I would like to know the answer to this too. I think WPP does allow recurring payments and CC data storage. I hear services like Chargify (http://chargify.com) are very useful to get up and running quickly (if you already have a merchant account).

Here's my list of bookmarks from earlier discussions on the subject on HN:

http://news.ycombinator.com/item?id=1392842

http://news.ycombinator.com/item?id=33322

http://news.ycombinator.com/item?id=526517

http://news.ycombinator.com/item?id=1206993

http://news.ycombinator.com/item?id=12010

http://news.ycombinator.com/item?id=175186

http://news.ycombinator.com/item?id=294120

http://news.ycombinator.com/item?id=598920

http://news.ycombinator.com/item?id=530055

http://news.ycombinator.com/item?id=1065419

http://news.ycombinator.com/item?id=975301

http://news.ycombinator.com/item?id=616417

http://news.ycombinator.com/item?id=526517

http://news.ycombinator.com/item?id=1381918

http://news.ycombinator.com/item?id=432284

http://news.ycombinator.com/item?id=526517

http://news.ycombinator.com/item?id=948036

http://news.ycombinator.com/item?id=1515677

http://blog.meatinthesky.com/introduction-to-online-payments...

EDIT: If you are based in the US, you have a lot of options to choose from. I'm in the UK, for which I find it slightly more difficult to find information.