I am interested or I am interesting - Participial Adjectives

Some words can form two adjectives, such as interesting and interested, concerning and concerned, worrying or worried. (For those who are interested in linguistic terminology, the ones ending on –ing are based on the present participle, the ones ending on –ed are based on the past participle of a verb.)  

Although these forms sound very similar, their use is different: 
if you say that you are interested, you indicate that something else is of interest to you.
If you say that you are interesting, on the other hand, you say that you are of interest to others.

The following page explains the difference with the help of many different examples that make it quite easy to understand:
http://www.grammar-quizzes.com/passive3a.html

The explanation on this page is less comprehensive and clear, but it offers a convenient list of approximately 20 word pairs that work according to this pattern.
http://www.geocities.com/Athens/Olympus/7583/partadj.html

The BBC page concentrates on the difference between ‘concern’, ‘concerned’ and ‘concerning’ and explains these in great detail. 
http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv183.shtml

Online quizzes to practise:
http://esl.about.com/library/vocabulary/blinged1.htm
http://a4esl.org/q/h/fb012-ld.html
http://www.angelfire.com/wi3/englishcorner/grammar/Interactive/prpartvpspart1.html
http://www.angelfire.com/wi3/englishcorner/grammar/Interactive/prpartvpspart2.html