My Chinese teacher told me that I need to work on my Pinyin tones, it's pretty difficult. I was looking through internet for some exercise for this purpose.
I have a Mac. It turns out that there are many cool and free learning Pinyin tools out there. This is the one you should check out if you are bad with Chinese tones like me:
Pinyin Table, Pinyin, pin yin, hanyu pinyin
They have Chinese Pinyin quiz. They will play a sound and ask you what tone it is... really neat.
P.S.There is also a Pinyin table, the site claims containing all Chinese Pinyin sound(is it possible?).