Kill Some Time

http://addictinggames.com/curveball.html

I can't seem to get past level 8. To put some english on the ball, make sure your mouse is moving when you hit it; this is particularly advantageous when serving.

Can anyone get to level 9?

When that one gets boring, give this one a shot...

http://addictinggames.com/gravball.html

There are only 20 levels and it's actually not too difficult to beat them all.