The C.S. Lewis Society of California has such a strong presence online that it is impossible to provide an adequate description of all their resources here because the purpose of this feature is designed to merely provide a short summary of other places online worthy of you attention. That said, not all the sections within their site are equally useful; but, then again, that will depend upon what you seek.
From the main page they presently feature brief details and a link to their latest free newsletter called “Logos” (which is also available by email). It comes out two to three times a year and is always full of a lot of useful recent news and links to Lewis related material. If you want a chronological list of Lewis’s books, along with an arrangement by subjects then their BOOKS area is the place to visit. It also has an exhaustive list of books about Lewis in the same place. While there are several other sections, the last I’ll mention is the ARTICLES area. It not only has links to a wide variety of articles about Lewis, but also has links to several essays BY Lewis that are posted online.