Here you have some links with exercises about the comparison:
Comparatives:
http://www.english-zone.com/spelling/comp5.htm
http://www.agendaweb.org/exercises/grammar/comparison/comparison-write-2
http://www.perfect-english-grammar.com/comparative-adjectives-exercise-1.html
http://www.learnenglish-online.com/grammar/tests/comparativeadjectives2.html
As usual, I'm waiting for your comments.
