Tha Russian way up north I think was the Tsar Bomba, the biggest one ever.
Biggest four ever done were in that area in 1961. Biggest US one was Castle Bravo at Bikini in 1954 at 15Mt and that one was the fifth biggest. The histroy of most of them can be found at
The Nuclear Weapon Archive - A Guide to Nuclear Weapons
With photos and some video.