I've been invilved in C&R collecting for the past 4 years, but for the past year I have been drawn to ads for AR15's and clones.  Now I've just got to have one.
The problem is that I know diddly squat about them.  Just browsing thru AA and Gunbroker confused me with all the different terminology.  The last time I handled one was in 1968 in AF basic training.  I need to be able to make an informed purchase, and know about the rifle once I get it home.

SO.........which book or books does this group think would be the best to get me acquainted with the AR15 and it's variants?  

Stan

The Black Rifle and The Black Rifle II

They are not cheap, but they have the best history (and lots of good photos, especially of rare variants and prototypes).  Lots of insights into the why's and what's.

If you're more into the technical apspect (i.e. how to build/repair) then the -23&P is what you need (and you can download it for free from this site - look in the Information button).

If you're looking for a general operations manual (field strip, clean, lube etc) the -10 is also available for free download from this site.  Jim Crew's Some of the Answer:Urban Carbine is another highly recommended book for the basics on rifle operation, shooting stances, etc.