Blues are the basis to many styles of music. The basics of blues piano lessons consist learning the "12 bar blues" and the blues scale. These two things provide you with the ability to improvise and play all sorts of neat things.
There's one site that has a number of free blues lessons for free. It's Play Piano Today's Blues Lessons.
To begin learning the blues, check out these blues lesson videos also. (By Music Guru 12 on youtube.)
The blues scale for beginners.
Here is a more advanced version on the blues scale
After you know about chords, check out this video on the 12 bar blues
and learn a boogie woogie trick.