Weak x4: Fire
Weak x2: Fighting
Neutral to: Bug, Flying, Ground, Ice
Resists x2: Dark, Dragon, Electric, Ghost, Normal, Psychic, Rock, Steel, Water
Resists x4: Grass
Immune to: Poison
Sporting 11 resistances and only 2 weaknesses, complete with 74/131/116 defenses and a potentially crushing movepool, 'Nuttre' could put a dead stop to many threats, old and new. He also has access to Spikes, Leech Seed, Curse, Explosion and a handful of other moves that any pokemon with similar bulk would only dream of.
With resistances to water and rock and a hardy 131 base defense, Nuttre almost seems like a better counter to Gyarados than even Celebi! Especially since it's not weak to bounce. It's also one of the few pokemon to resist both Water and Electric... and alot of the types listed above actually. You'd think grass/steel would be similar to bug/steel but the resistances they bring are actually extremely different.
With only 2 weaknesses, and to type's that are commonly seen on the same pokemon, Nuttre's counter's will likely be easy to shut down, and it seems he would make an amazing partner for Shanderaa, Burunkeru, or almost any ghost type!
(Thanks to Kyu for move info and weaknesses/resistances!)