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.