From staging (or development) to production (or live) server.
Candidates: http://wplift.com/wordpress-development-site
RAMP (solution)
http://crowdfavorite.com/ramp/
5 Quick and Dirty Steps (the dirty way)
http://archonic.com/blog/web-mastery/wordpress-staging-in-5-step/
DeployMint (solution for Multisite)
http://premium.wpmudev.org/blog/introducing-deploymint-a-staging-and-deployment-system-made-for-wordpress-multisite/