You dont really need a "task killer" app mate, they do more harm than good. If you feel your phone getting bogged down, all you need to do is clear your memory using the standard multitasking button, that is it. And maybe clean the app cache to free up memory if needed.
Never felt the need for a Cleanmaster type app. If clearing your app list through the multitasking button does not work, a simple reboot will usually do the trick.