Many clearly explained lessons from Acousticguitar.com.
Cyberfret.com has very useful lessons on chords, strumming and more. It includes videos, charts and more.
The lessons available from guitarists.net are also well done and some are available in printable format.
More useful lessons are found at guitar site.com . There are lots of resources here. Like some of the above sites, they explain the theory behind chord structures and playing.