F.A. Afanasiev "Poeticheskie Vozzrenia Slavian na Prirodu" The book was published in 1886, I guess, and it is incredibly hard to find, although "Indrik" publishers (Russia) rolled a second edition in 1995. This is a three red thick volumes series. The book is considered a classical reference to ancient Russian folklore.
B.A. Rybakov "Yazichestvi Drevikh Slavian", Moscow, 1982
B.A. Rybakov "Yazichestvo Drevnei Rusi", Moscow, 1984.
These two are full-scale scientific monographies.
"Pesni Ptitsi Gamaiun" It contains the material, part of which is included to "Dazhdbog's Grandchildren". The "Pesni" is a poetic recreation of the Russian pagan mithology by A. Asov.
Works of Yuri Miroliubov. This is 6-volume series. Miroliubov was exiled from Russia after 1917 but continued his research (mostly based on the material from life of southern Russia). He had a notebook where, during his life (he died in 1976), he collected a lot of material about Russian pagan history. All these materials and his personal work on The Veles's Book were used in his reasearch. Miroliubov also dreamed to write a poem about the Great Prince Sviatoslav -- the last pagan prince in Rus. He succedded, and a two-volume poem is published separatey. However, reading his books can be difficult for a foreigner because throughout the books he hopes you know many things from Russian customs, traditions, Russian ancient history, ancient Slavic languages, etc.

Sergei Lesnoi, Otkuda Ti, Rus?. "Donskoe Slovo" publishers, Rostov-on-Don, Russia, 1995.
This is a result of the life research made by Sergei Lesnoi (real name -- Paramonov) and completely devoted to ancient Rus, pagan beliefs, etc. Printed originally as The origins of the Ancient "Russians", Winnipeg, 1964 because Sergei lesnoi was among those Russians who left the country after the Bolshevik Revolution in 1917. The book starts with the extensive review of facts proving that a viking-based theory of Russian origins is wrong. It also contains a consistent analysis of the available data on history of Rus, languages, etc., gives original texts of the "Veles' Book".
Maria Semionova, Mi -- Slaviane!. "Azbuka" publishers, St.-Petersburg, 1997 Maria Semionova is a known Russian writer. She specializes on books about ancient times. As a part of her reseratch to present this life in a true and consistant fasion, she collected a lot of material about ancient Russians and presented them in a very structured and interesting way. The book talks about religion, day-to-day life, building construction, weapons, etc.