Need some suggestions on the best general reference book on the AR15. It needs to have maint. tips and maybe a listing of trick parts.

"trick parts"?  That would be The Ricer's Guide to the AR-15.  

For actual maintanence, go to this site's Info Library and look under Guides.  You'll find everything you need to know about keeping an AR running properly.

Under Books, The Black Rifle: M16 Retrospective is considered by many to be mandatory reading for anyone who likes ARs, so an owner/operator of one ought to beg/borrow/steal a copy sooooon.