My personal favorite tweak of all time is KillBackground. I use it all the time, always after quitting a few applications, or exiting out of music app or even after playing a game, KillBackground lets me remove the recently used applications still running in the background and draining your battery life.
There are a few simple options that come along with KillBackground. You can set it up for your iPhone/iPod and even for iPad.
"Button on the left" toggle will display the KillBackground button on the left side of the screen. When the toggle is off, the button will be on the right side. I always like to have my button visible and my switcher to automatically close after tapping on it, as well as killing music automatically after listening to whatever you had playing. Big buttons will pop 2 buttons on both sides of the screen, very useful when on iPad.
On the left is how I have it setup, with the button on the left side of the screen, and on the right 2 big buttons for iPad users, simply making it an easier access to the tweak itself.
KillBackground is a free tweak made my Mathieu Bolard (mattlawer) under the BigBoss repository. As always, you can follow me on Google+ and Twitter, and please share my blog with your friends. Sorry to keep you all waiting, I had a long day today. More to come soon :)