Ernest Pergrem'sTI99/4a Book Archive.  If you are looking for a reference to the TI99 or just a really cool and well done site then click here.  Ernie is one of the great underground guys.  Very helpful and most knowledgeable.

Mainbyte's ti99/4a pages. A ridiculous amount of information presented in a very friendly manner.  Got my start by using these pages.   For hardware heaven go here. Actually more than hardware but the hacks section is incredible ! 

The TI Tech Pages.  A bit intimidating at first but extremely accurate, in depth technical information relating to the TI99, it's hardware and software.  May take a while for some of this heady stuff to sink in but this is the lair of a genius after all.  To get smarter by osmosis go here.

The TI99 Timeline. If your a history nut or is in need of a factoid then Bill's site is for you.   To get the straight story go here.