No such thing. If your phone is lagging you either have some apps that aren't shutting down properly or are hogging resources. Go to menu > apps > running and see what's using all the memory. At the bottom you should see how much free RAM you have. If that number is low, you probably have some apps running in the background that don't need to be. The Android OS is very efficient at managing memory, but not perfect. Some apps are poorly designed and instead of going into standby, they run in the background.
Don't get a task killer or any kind of memory manager. At this point they can only cause problems. If you have apps that are poorly coded, get rid of them. Are you running a 3rd party launcher or the stock launcher? Sometimes 3rd party launchers aren't the best.
The easiest thing to do if your phone is lagging is to simply turn it off and back on.