University College London
University College London: Adverbs
This grammar site sponsored by University College London features an entire lesson on adverbs and an exercise to test your knowledge.
University of Calgary
University of Calgary: Parts of Speech: Adverbs
This site has good information on what adverbs are, what they do, and how they are used. Very helpful links to other information as well.
University of Calgary
University of Calgary: Parts of Speech: Distinguishing Adjectives and Adverbs
This site helps you distinguish between adjectives and adverbs.
University of Ottawa (Canada)
Hyper Grammar: Modifiers
Explains when and how to use adverbs and adjectives properly. Also includes a short section on conjunctive adverbs and their rules of usage.
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.