University of Victoria (Canada)
University of Victoria: Adjectives and Adverbs
This is a basic explanation of adjectives & adverbs, with examples of each. This resource explains how to change adjectives into adverbs through interactive exercises (with hints and answers).
University of Calgary
University of Calgary: Comparatives Superlatives
This site, sponsored by the University of Calgary, has a lot of good information on comparative and superlative adverbs and adjectives. Examples are given and a quiz is provided at the bottom of the page.
Other
Using English: English Language Quizzes
Over 200 short self-quizzes for English learners at beginner and intermediate levels. Quizzes span topics including spelling, grammar, vocabulary, and punctuation.