Aimless' recommendation on that book is a great place to start. The reading isn't dry at all and will further give you the "itch".
There are so many great manufacturers of complete rifles and recievers that you can spend some time looking into "ALL" of them (if THAT is even possible)
As far as some brands off the top of my head that are excellent are: (IMHO)
Bushmaster (But costly, however, great product)
Armalite (Same as above)
DPMS (great quality, slightly less in price)
Rock River (Top quality, BETTER price)
Lauer (Excellent quality, great price)
Stag (Ditto)
Ameetec (Ditto)
ASA (Stripped lowers are great, Uppers have been reported to be problematic. Price good however, the company is now out of business. Some ASA lowers still available in different places, you'll need to call around. (Made my LMT -IRC)
Olympic (I am not a big fan of them, but others are. Decent pricing)
The above is but a SHORT list of what is available and again, off the top of my head. Take a look at the AR15 discussion sub-forum and look at the photo threads and you will see so many variants, it won't be hard to imagine your dream build first AR.
Oh, and just a heads up, get ready to part with some serious cash over a long time as there are always "bigger and better" parts, you'll end up re-configging many times as there is always new stuff for the AR all the time and we even make it easy on ya! Enter the EQUIPMENT EXCHANGE, all the resource you need to go BANKRUPT!
Welcome to the addiction that unlike drug addiction, cant be treated or cured.