Russian - mainly Zenit - cameras. Has an article on Zenit disassembly.
A BIG site with lots of info on the above.
A very interesting reading on the origins of FED cameras. You will enjoy it even if you don't intend to use or own a FED.
Includes disassembly and repair of a Zorkij-1 and its collapsible lens.
A great site with lots of info on Zorkij-s and FED-s, especially the FED-2. Nice examples of home painted black cameras. [Jan-07 Sadly, this link is no longer valid.]
Apart from cameras, useful advices can be found here on general camera repair (tools, materials, techniques). [Jan-07 Bummer, this site is gone, too.]