If you're looking for other websites dealing with the TI-99/4A, by all means have a look at Rich Polivka's site. It is a gold mine of information, most of which is easier to understand than the "geek-chow" you'll find here.
In addition, Rich has a large link-page, with links to almost every website dedicated to the TI-99 (4 and 4A). It would be pointless for me to reproduce (part of) it in this page, so I guess I'll just refer you to it. Just follow this link.