Confusing Words.com: A collection of 3210 words that are troublesome to readers and writers. Grouped according to the way they are most often confused or misused.
ESL-Lounge.com: Online vocabulary quiz for intermediate students. Bored or Boring? Practice of -ing/-ed adjectives. 14 questions. Answer keys for this exercise can be found at: http://www.esl-lounge.com/level2/lev2boredboringans.shtml.