Two families of tobacco hit me with a lot of nicotine: the Tanzanian Virginias and strong Burleys.
Gawith ropes and flakes are a good place to go for the first group. Any of the brown twists are potent, as are 1792 Flake, Dark Flake, etc. Dunhill Royal Yacht is another classic blend in this group.
As for the second, I've tried Five Brothers, C&D Big and Burley, and D&R Picayune. All of them are quite potent.
Lastly, blends like Irish Flake have a little of both, and pack a kick as well.