This is an old thread, but some of us would rather search the old stuff rather than asking the same question again so I'm updating with my information. (Disclaimer: I'm still in the researching phase of this, so this is not experiential knowledge)
There are 4 types of peanuts, all of which are nitrogen fixing.
1) Runners reproduce obviously by runner. They are consumed salted or ground into peanut butter.
2) Virginias are either bunch-type or runner. They are large "fruit". They are roasted or served in the shell.
3) Spanish are bunch. They are small "fruit". They are frequently processed into things like candy and peanut butter.
4) Valencias are bunch. They are sweet and are either roasted or served in the shell.
While Wikipadia lists Tennessee Red and Tennesse White as separate types, other sources I've read list them as breeds in the Valencia group.
One good reference:
http://www.goodearthpeanuts.com/aboutpeanuts.htm