- Comparative: better
- Superlative: best
- Adverb: well - this is the only fully irregular adverb in English, all others are bare adverbs.
There is also an adjective goodly meaning "quite large; considerable; sufficient; adequate; more than enough"
Good is exceptional in that it accepts "no", "any", and "not much" in the simple adjective form as well as in the comparative: "This food is no good"; "The food isn't any good" / "the food isn't much good".