Chart of comparative/superlative forms:
another chart with explanations: http://english-zone.com/spelling/comparerules.html
Form Practice:
http://a4esl.org/q/h/vm/compsup.html
http://a4esl.org/q/h/vm/compsup2.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=1746
http://www.englishexercises.org/makeagame/viewgame.asp?id=4661
http://www.learnenglish-online.com/grammar/tests/comparativeadjectives2.html
Comparative with Adverbs:
http://www.englisch-hilfen.de/en/exercises/adjectives_adverbs/adverb_comparison.htm