The following are the basic riffs that you'll need to play blues harp. My goal here is to give you a basic understanding of what is going on in blues and what you can play at different points in the 12 bar blues cycle.

12 bar blues harp theory
Beginner's Practice Riffs
Faking Blues Riffs
Blues Harp Scale
Triplets
Help Me lick
Hoochie-Coochie Man and Mannish Boy Riffs
Peter Gunn Bass Line

Here are some simple harp tabs for songs. They are mostly not blues, but they are "Bluesey" with plenty of bends to practice.

Stormy Weather
Amazing Grace
Black Rat Blues Harp
Don't Get Around Much Any More

I've spent some time and tabbed out some blues riffs and phrases using a little javascript engine that I designed. This will allow you to play riffs in first, second and third positions. This is great for learning to really play blues harp.

B.B. King Sweet 16
Little Walter's Juke
Little Walter's Off the Wall
Born Under a Bad Sign
Cream - Sunshine of You Love

I spent a lot of time working out almost all of Help me by Sonny Boy Williamson II (Rice Miller).