1.  Passport America
2.  Happy Campers
3.  If you join http://www.fulltimefamilies.com, you get a discount to passport America & lots more
4.  Camping Club USA is the Camping World/ Woodalls club ~$39
5.  Harvest Hosts is a yearly membership...while the overnight is free... Last year it was $20, I believe they've raised it to $30 this year.
     There are no hookups at all, just a parking spot. They don't expect you to set up camp, etc.
6.  FreeRvparking.com $25/yr organized updated database for free overnite parking (not so much camping)
7.  You might check out one of the thousand trails zone 1 year memberships.
     They are $475 a year with "free" camping 2 weeks at a time. There are restrictions so make sure you read them.
8.  There are groups like Escapees where you get an actual address and they will forward your mail to you.
9.  workamping positions