Our company makes wyBuild: http://wyday.com/wybuild/ . It comes in 3 parts (wyBuild, wyUpdate, and the AutomaticUpdater control). wyBuild makes the tiny update patches, wyUpdate is the open source updater (BSD licensed) and the AutomaticUpdater control is the open source control that adds the ability for fully automatic updates (LGPL Licensed).

Here are the links to the source code, for those interested:

wyUpdate: http://wyday.com/wyupdate/

AutomaticUpdater: http://code.google.com/p/automatic-updater/ (instructions: http://wyday.com/wybuild/help/automatic-updates/ )