I've been looking into Slavic Paganism recently and I was wondering if Eastern Slavs (such as the Russians) worshipped Perun. It seems that worship of Perun originated in Croatia and spread throughout the Balkans and to Western Slavic peoples (such as the Czechs) but I saw no mention of the Eastern ones.
Perun, the Thunder God, was one of the major deities in the earliest stages of the recorded history of the Grand Duchy of Kiev. In the Rus Primary Chronicle, it is said that when Vladimir became the Grand Duke of Kiev, in 980 AD, he erected statues to seven pagan gods in front of his palace. The Perun statue had a silver head and a golden mouth. When Vladimir converted to Christianity, in 988 AD, he order the statue of Perun to be dragged down to the Dneiper river, where it was unceremoniously dumped into the river.
Sources: http://www.shsu.edu/~his_ncp/PagKiev.html
http://perun.ca/History.aspx