In "Using Russian: A Guide to Contemporary Usage" Derek Offord and Natalia Gogolitsyna maintain that there are three broad categories of dialects within Russian --

1. The Northern Dialects (North of Novgorod)

2. The Southern Dialects (From the Belarus and Ukraine borders to Kolomna)

3. The Central Dialects (Moscow, Pskov, Vladimir)

They differ in matters of phonology, grammar, and vocabulary.

I mean, I suppose if equipped with an extensive background in linguistics, one could argue the merits of these categorizations (probably simply on the basis that we can't definitively define "dialect") but I'm sure the fact that Russian has "dialects," or at least marked variation, is widely accepted among Russian scholars, native speakers and otherwise.