Cruise the Lena or the Volga
One of the problems with tours and cruises in Russia is that most of them tend to concentrate on the two main cities, Moscow and St. Petersburg. They are both great places, but there is also a lot more to explore in this vast country.
For example, you can cruise on the Lena River in Siberia. This is the river from which V.I. Ulyanov acquired his work name of Lenin, because he was exiled near the river. The cruise is not cheap, but it will show you some very remote parts of the country. A 15 day cruise including air fare from London starts at about $3600.
Or for something a little warmer, consider the southern Volga cruise between Moscow and Astrakhan. This takes 14 days, again with flight from London, and rates start at about $2500. Ports include Kazan, capital of Tatarstan, Samara, Volgagrad where the decisive battle of World War II was fought (the city was called Stalingrad then,) and Nizhny Novgorod, among others.
These cruises and a number of other tours by land and river are offered by www.into-russia.co.uk, the successor to the former British branch of Intourist, the state travel agency in Soviet times.