I am looking for some weight lifting exercises for the area under the pectoralis muscles, namely the serratus and oblique. I heard this is beneficial for people who play basketball, volleyball and tennis...
Probably the best tool for the job is the ab wheel. It's a $10 piece of equipment you can get from Walmart, but you will need to work up to being able to use it. However, getting to using it in it's truly beast skill way is very difficult.
David Lasnier has some progression to get your abs ready for the wheel.