I wrote an app called Gauge Mathematical Tool that would be perfect for this. You can use it to calculate up to 10 Million digits of Pi, which as you would expect, really stresses the processor and memory, leading to short battery life. It can also be used as a benchmark to compare the speeds of two iPhones or iPod touches.
There's a link in my signature to its app store page.
lol, yea, probably.
Streaming MLB games from MLB At Bat would hurt my battery quick. Other streaming such as radio from Pocket Tunes or the ESPN Radio app will knock it down somewhat quickly too. These apps will cause my iPhone to get pretty hot too. I just heard about (and got) the UStream Viewing app today. I'm sure that would cause it to go down quick.