BJCP style guidelines.
Each style has an ABV range associated with it. I entered the number which falls in the middle of the low and high ABV for each category. For example, a Baltic Porter will have an ABV between 5.5% and 9.5%, so the "average" used for this illustration is at 7.5%. Of the 72 categories with listing for ABV in the style, the illustration shows those with 6% or higher ABV.
The biggest bang per ounce will be found with an Imperial Stout, Barleywine, or Eisbock. Drink with care.
Here is another way to look at it, showing the complete range within each style.