Umpire Instructional Materials

[Buckeye12]

I am wanting to compile a collection of instructional umpiring materials to start a "library" for our local high school association. I am wanting books, DVDs, videos, CDs, cassettes, etc. that would be beneficial to our membership. Does anyone have any suggestions of quality material that would be a good addition to this collection? What are some of the best materials that you've read or watched that are well worth the investment? Links to the material would be helpful, too. Thanks!