I just picked up a couple of excellent books from Amazon that I highly recommend for those interested in Soviet/Russian warplanes.
The first is called "SU-27 Flanker Story" by Andrei Fomin. The book has a ton of information on the development of the SU-27 Flanker, and its fielding. Amazing, in-depth explanation and photos of the many prototypes of this aircraft, as well as its various sub-systems. 336 pages of everything you wanted to know. It also covers variants, from the Naval version (SU-33), to the advanced versions (SU-35/37) to the fighter-bomber (SU-34). The book was published in 2000, so it does not have any information newer than that (so nothing on the newest SU-35 without canards, etc).
I was not surprised to find out how much the Soviets followed the F-15's development when designing the SU-27. They "acquired" engine blueprints, radar, avionics and other info both through espionage and open-sources. The author does not delve much into this aspect, but the topic came up at several points.
ISBN 10: 9785935110032
The second book is called "Russian Air Power" by Yefim Gordon. Yefim Gordon is an expert on Soviet/Russian aviation and it shows in this book. The book has detailed information on various planes ranging from cargo planes, fighters, bombers, to trainers etc up to date as late as the 2008 war in Southern Ossetia (Georgia vs. Russia). There's a lot of info on the various units using each type of aircraft, and a wealth of information on the history behind these organizations. Gordon has a lot of other books that are hard to find and out of print, which cost around $200, but they are a great addition to any enthusiast's library. I am holding out for some of the other ones, hoping I can find them at Half-price books or somewhere else for less than $100.
ISBN 10: 9781857803167
There are reviews of these books available on Amazon and elsewhere. I can't do them justice. Together, they cost me about $100, and I think they were well worth it.