There are many resources giving information about motivation and the authors listed on this site. Here are a few to get you started:
For more information about Keller's ARCS model:
http://www.e-learningguru.com/articles/art3_5.htm
http://www.ittheory.com/keller1.htm
For more information about E.J. Sass:
http://honolulu.hawaii.edu/intranet/committees/
FacDevCom/guidebk/teachtip/motiv.htm
Sass, E. J. "Motivation in the College Classroom: What Students Tell Us." Teaching of Psychology, 1989, 16(2), 86-88.
For more information on Howard Gardner and Multiple Intelligences:
http://www.infed.org/thinkers/gardner.htm
http://www.nea.org/neatoday/9903/gardner.html