How to see what apps are slowing the iPhone down?

Jail broken or not, is there a way to see what apps are using so much RAM and causing force closes in apps?

If you go a Iphone 4g and higher you can tap the home button 2 times and all the apps there are oped, You have to close then. To do that you click and hold the app and their will shake a pop out a "X" on the top left just click it and it will close, That should make the Iphone faster and not be slow.

I would look at the running apps and how much memory they are using first, then that will give you a better idea which ones to consider removing.