There are obviously a number of books available and it really depends on what era captures the heart most, personally its the 30's and 60's when I feel Alfa where at their finest.
There is a nice book called " The Alfa Romeo Tradition" by Griffith Borgeson that gives a broad feel and which deals not only with the cars created but the most important men at Alfa Romeo throughout its lifespan so to speak which is interesting!
It has both colour and black and white photographs and I think can be purchased at a discount from Mill house books along with many others For Alfisti.
Another you may find of interest(if still available) is I think "The Alfa Romeo Museo" which is only thin but basically documents the Alfa musuem in Italy with most of the cars that reside their it only cost a couple of pounds and has a few beautiful 2.6 pre war cars etc if I remember correctly, just nice to own really!
This is not a history book, but I strongly recommend it anyway: Bill Braden`s Alfa Romeo Owner´s Bible. It has technical stuff, but mostly on a practical level. Engine development is interesting to read, for instance, even if you are not planning to do a major overhaul by yourself.
Yeh forgot about that book it is an excellent choice. I See you have a 90 wonder if that is the only one here! Always admired them greatly, lovely understated but somehow cleaner lines than the alfetta, real gentleman's Alfa somehow and probably the most exclusive modern left still packing the 6 shot to!
The author of the book AR Owner´s Bible is Pat Braden. Sorry, I got the name wrong.
I agree that the 90 is a very beautiful car, but so is Alfetta. Cleaner lines than those of 75. I drove it exclusively from 87 to 99, but it had a four cylinder engine then. A very good car in practical daily use.