The Kiev family, lots of different small variations from types of plastic used on later 303s, different body paneling to different white paint shades of logo (yeah I know you're gonna laugh at that

http://www.ussrphoto.com/UserContent/1992016_vHaz6bxtCuw.jpg
The Agat family, there are numerous combinations of different types of shutter button, lens ring color and body color:

http://www.ussrphoto.com/UserContent/1992016_MlLGDRdaacM.jpg
3 different types of cyrillic logos on Sputnik:

http://www.ussrphoto.com/UserContent/1992016_f-wM7_65l3A.jpg
I hope I didn't scare you
Cheers,
Vlad