Does anyone know of good websites that explain the different methods of funding health plans, describe how premiums are set up differently, etc... Something that discusses HMOs, self-funding arrangements, intermediate risk sharing arrangements, risk pool type arrangements, etc... Thanks!

The Society of Actuaries website http://www.soa.org/
and the American Academy of Actuaries website http://www.actuary.org/

will lead you some of their publications

Under the Society's Education section, review the Study Notes and reference material for the exams on health care; and on reinsurance and risk.

from the Academy's website, you should be able to locate monographs published by the Academy (and Society) concerning funding of health care and Medicare.

I am not sure whether these publications are available directly from the site or if you will need to purchase them in hard copies.

And here is a brief online article (requires Adobe Acrobat Reader):
http://www.grsnet.com/rr990401f.pdf