you do not need any task killer...all you need is the power control widget that comes with the phone. keep all those things turned off when your not using them, if you still have a batt. problem you probably installed a poorly written app.
that is the main thing - anyone can make an app for these phones. it only takes one poorly written fart sound board (or whatever) app to drain your batt. in a matter of hours, send you phone into a boot cycle, or numerous other things. you have to read comments and use the star rating to determine if it is something you really want on your phone. also before you install an app it gives you a list of resources that app will have full access to...if you are d/ling a fart sound board and it wants full phone/network access you probably wouldn't want to d/l that
and if you really need something to kill processes and whatnot...get Astro file manager it has a task killer (that only kills when you tell it to), app manager/backup, and is one of the best file managers out all in one app