Domain and hosting reseller program. Starts from $100 signup and prices drop as the total lifetime spending on the account increases. Interesting model, competitive pricing. Ability to resell.
Community Server is a white label social networking platform. It runs on Microsoft .NET / IIS technology. It powers the MySpace Forums and Microsoft's adCenter. Starts from $3k per year (small site), $50 per seat (min 200 seats) or $20k per server.
Amadeus offer a range of travel related services including white label travel search engine.
Social Engine is a white label PHP based social networking platform. You can implement your own plugins around their architecture. Basic costs $300 plus $290 for all the plugins ($30 or $40 each) as at June 2008.
KickApps is a white label social networking / video hosting platform. Free to sign up, ad supported, or you can buy the ads out, starting at $100/mth for 5'000 page views.
Dotster offer white label domain name registration and hosting services. The interface is fairly slick. Could be useful.