Here are a few additional websites that you may find useful. I am not responsible for the content on these sites.
*Note: Since there are no more official websites for the TI-81, -82, -83, -92x, or -85, the links are to Wikipedia pages.
http://www.ticalc.org/-Very well respected (and highly trafficked) website with programs, information, and guides.
http://www.prenhall.com/esm/app/calc_v2/frameset_83.html- General mathematics functions on various TI products