General info
Camping.com has articles about snowbirding, places to in various regions, etc.
Gorp.com links to many campgrounds in North America.
http://www.happyvagabonds.com/ has info and links to work-camping, and some boondocking info.

Campendium.com list camping all over the country, sorted by place, type, etc. Looks very useful.

Full-time RVing
CampHalfPrice full-timing links has links about full-timers.
http://gypsyjournal.net/some_of_our_favorite_rv.htm is a list of RV groups online, and also a lot of other links to RVing.
http://seniortravel.about.com/od/rvtravelroadtrips/qt/lowcostrvplaces.htm has info about low-cost places to stay with an RV.

Camping clubs
http://www.rvlifestyleexperts.com/free-rv-info/getting-started/membership-rv-parks/ Membership parks and camping clubs: are they worth it?
http://www.frugal-rv-travel.com/RV-Membership-Clubs.html Best RV Membership Clubs for Boondockers. Large list of clubs.
http://www.rv-clubs.us/ lists clubs and a lot of other links and lists of other RV things. Shows, rallies, magazines, and a lot more.

Escapees RV Club is full of RV lifestyle info. The forums are great. It's a club with discounted camping and fixed lots.
http://www.camphalfprice.com/ is $40/year and has 1200 member campgrounds.
http://www.passport-america.com/ is $44/year and has lots of campgrounds and other benefits.
http://www.campingandcampgrounds.com/ is $44/year and offers discounts.
http://www.explorer-rvclub.com/index.html is a Canadian club.
http://www.goodsamclub.com/ is Good Sams Club, camping discounts and a lot of other benefits.

Government lands
Senior Pass A $10.00 lifetime pass that provides access to more than 2,000 federal recreation sites. Also discounts on fees and activities such as camping. This replaced Golden Age Passes.
http://www.fs.fed.us/passespermits/ US Forest Service camping.
http://freecampsites.net/snowbird-season-is-here-stay-warm-with-free-camping-in-the-southwest/ offers a few places in the southwest to camp free or almost free.

Boondocking
http://loveyourrv.com/love-your-rv-boondocking-basics/ is a good article about dry camping, with some nice pictures.
http://www.telusplanet.net/public/waters/index.htm is a guide with destinations, routes, BLM info.
http://www.boondockerswelcome.com/ Free boondocking on private property.  Membership required.
http://www.harvesthosts.com/ More free boondocking on private property, wineries and agricultural sites mostly.  Membership required.

Wheeling it boondocking for newbees part 1 | part 2 | part 3 | part 4

http://www.rv-adventuring.com/quartzsite.html Quartzite Arizona info.
http://www.boondocking.org/ has a database or free camping spots around North America.
http://cheaprvliving.com/Boondocking.html discusses boondocking and living very cheaply. Some good info.
http://cheaprvliving.com/ExtrasForTheGoodLife.html is a guy who lives in his motorhome.
http://www.frugal-rv-travel.com/index.html is about living in an RV, mostly boondocking.
http://www.overnightrvparking.com/faq.php lists thousands or overnight spots for dry-camping.  Membership required.