The following is a list of links to dry hopping and late hopping resources on the internet. I'll continually add to this list as I find more resources. If you know of others please post a comment here with a link. If you are interested to see what other resource pages I have created click on the "resource posts" label link at the bottom of this post or over there in the sidebar.
If you are looking for books about home brewing...
Brew Your Own - Dry Hopping Techniques
Main Street Homebrew Supply Co.
My first experience with dry hopping with hops that Bryan and I grew.
Ted over at Ted's Homebrew Journal passed along this link about late hopping.
Aussie Homebrewer: filter out hops leaves before they get to the keg...