Hey there. I'm going to make this short and sweet since it is getting close to 1 am in my neck of the woods. Perhaps I need to meet with a group SBA (Scuba Board Anonymous). Here's a short list of excellent online materials I've found. I believe that when you take formal training the key is to have knowledge so you know why you are being taught some skill in particular "not just because your instructor says so". It helps understanding the practical skills and you'll sound smarter in class
I've put them in order so they logically progress if you start with the first ones listed then the second etc
Without further ado:
Read this one first it introduces nitrox, some basic physiology, and some other gas mixes like trimix (aka voodoo gas,i love that one) :
http://www.gasdiving.co.uk/pages/misc/Nitrox.htm
Then this fella's got some good things to say scroll down to the contents and read everything from "Nitrox and Air" to "Going Deeper and Tech". Don't read his version of "Decompression Theory" since it is a crude rewording of Paul Chapmans article listed just bellow. Please keep your mind open to DIR he doesn't think much of them but DIR has great philosophies
http://www.njscuba.net/gear/index.html#Contents
Then on to algorithms (ZH-L-16) "How are those rudy tables created?" This is a great and well referenced article by a british chap called Paul Chapman and is a must read. Download it and read and revel in your new found knowledge.
www.vvw.be/duiken/zhl16.doc
FREE DOWNLOAD: Watch the entire DIR III video at this link:
http://www.deepsouthdivers.org/DIR3.html
The following is just a GREAT read about a guy and his tech training experiance:
http://www.scubadiving.com/training/specialty_and_advanced/attitude_adjustment/
This link has many great articles, though perhaps not really technical in content, they are very informative. Take some with a grain of salt and like usual keep an open mind:
http://www.scubadiving.com/diving/specialty_and_advanced
After reading all that if you are hungry for more you can go to the WKPP website wkpp.org and download a pdf version of most of their manuals for a MUCH smaller amount of money then the other books listed (not that they aren't valuable tools as well). FUN reading. Guess it wasn't short and sweet after all.