I found this web site awhile back as I was trying to bring myself back up to speed on the hobby after being out of flow of things for a number of years.
http://frrl.wordpress.com/He calls his web site "The most eclectic Amateur Radio site on the Internet."
The link below is to a paper that he has on receiver princepals. I found it to be one of the most concise and readable that I have seen so far. It is really good reading especially for new hams.
http://frrl.files.wordpress.com/2008/08/principles_regeneration.pdf