Memory: Per app

Would there happen to be a memory app that shows how much ram each app is using and maybe even allow for it to be purged? I know there are tons of apps that claim to optimize your memory in the background, but knowing which of your apps eats the most ram would be ideal and helpful (adjust settings, etc.). Something along the lines of a task manager...

I've been closing the apps through the menu option, rather than using the escape button, but there still seems to be something eating up memory - and relatively fast.

Any suggestions would be appreciated, thanks!