Here are some more.
Books on Charles Cameron, architect at TS and Pavlovsk
Nicholson & Watson – The Commodore Press, London 1943
Out of Print but not too expensive
This book was published during the war and was meant to bring Cameron to the attention of the English. I personally found some inaccuracies in the text, but it is illustrated with good quality prewar photos. (I thought this book might be on line here, but I don't see it. Does anyone know?)
Charles Cameron: Architect to the Court of Russia
Elek Books, London 1971
Out of print. Reasonably priced
Probably the most in-depth book around on Cameron with a detailed and informative text, though few illustrations.
The Empress and the Architect: British Architecture and Gardens at the Court of Catherine the Great
This fantastic book begins with Charles Cameron’s work for Catherine the Great and expands from there to look at other styles and movements in Russian architecture at the time, including Neo-gothic, Orientalism, and Neo Russian. The book talks in depth about Adam Menelaws and William Hastie among others. There is a considerable amount on Tsaritsino and other complexes. The book is beautifully illustrated with modern and archival photos as well as wonderful architectural renderings by the architects involved.
Imperial Palaces in the Vicinity of Saint Petersburg: Gatchina Pavlovsk Peterhof Tsarskoe Selo
Emmanuel Ducamp, editor. ISBN 2909838013
These four volumes (which were also sold separately) are primarily very high quality reproductions of watercolors of the palaces, both exterior and interior. The set is rather hard to come by and the publisher went under shortly afterward (so I'm told). A complete set can easily cost over $200. Be careful if you try to buy it as it isn't always easy to tell if the whole set is for sale or just a single volume. All my copies have the same ISBN number. I'm not sure if it is different for the individual volumes, but I imagine it is. The picture Vladimir posted shows a different cover than what is on my volume, so I'm assuming his isn't part of a set.
I've still got a bunch more to post; I'll get to them soon. Hope I'm not boring you guys with this.