@Steelie, I have been running a couple of different ones to get a feel for it. Advanced Task Manager Free is what I am using, but for the issues your having, what you have to do (and this is with most task managers) is after you install it, reset your phone, start any apps you would usually want running (just go in and back out of them) and then open ATM from the All Programs screen, and click every app running and select "Exclude", then do the same under the Service tab.
Now anytime you wanna free your mem without messing up what you usually run (or what's vital) you can now happily hit that kill widget on your home screen
There should really be a sticky for this or it's probably in the tips and tricks section because it's what you should do with any task killer.