Links

Videos

Series and Sequences  (time: 6:18)
http://www.youtube.com/watch?v=G-3NvzYmNZs

Geometric Series (time: 5:28)
http://www.youtube.com/watch?v=rOX2Wk_0smQ

A discussion of summation notation is given:
http://www.youtube.com/watch?v=hEPk36Yncxg

History

This is one of the best all around sites that I have found. It is titled "The MacTutor History of Mathematics Archive."
http://www-history.mcs.st-and.ac.uk/~history/

This is an award-winning site that links to all sorts of mathematics information.
http://archives.math.utk.edu/

Reference Topics

A primer of summation notation can be found at this site:
http://www.columbia.edu/itc/sipa/math/summation.html

Here is a practice site working with arithmetic and geometric series:
http://mathforum.org/sum95/math_and/spreadsheets/examples/series.html