Welcome to Android!
Unlike other operating systems, usually nothing needs to be done to manage apps as you would with other phone operating systems.
The mechanisms you need are built-in and automatic.
People push task killers because the list or running apps appears
high and as if things never stop, but that's not true. Things not being used are put to sleep (so you can re-enter those apps super-quickly) and if left alone for a while, they're replaced with a little file that explains how to re-start them almost as quickly (you won't notice the difference on your dual core magic Photon
). Left alone even longer, Android simply removes them from the running process list altogether.
Priority operating system services and phone apps - Android knows to never kill those.
App managers will scare you into believing that all sorts of things are running that really aren't - and using task killing will simply confuse the operating system's automatic mechanisms and end up taking more resources and battery life than you might think you're saving.
Killing an app is only a good idea when you're troubleshooting the idea that you might have a rogue app (bad install, bad configuration, or just a plain old crappy app). And when you're at that point, you're doing best if you're on your way to getting rid of the bad app and restarting your phone to recover from it. (I test a lot of beta apps myself, so I speak from experience on rogue apps.
Here's a link to the whole shebang in the Evo 3D forums. It has a _complete_ explanation from an Android app developer (alostpacket) discussing this, as well as an Android expert (SirSlayer aka Slayer69, also a developer) who backs this up with links to articles from other experts.
Memory and task management
The only thing you want to track (for killing), aside from the cases I describe, are your Sprint bloatware apps. Those are apps that you may not be able to remove without gaining administrator access to your phone (aka rooting your phone).
Even then, only kill bloatware when it's clear that you've gotten our help in how to use various monitoring tools (all free in the Market, but tricky to use for newcomers only at first) - and only when it's really clear that the benefits of killing that bloatware outstrips the negative effects of task killing.
To really see how little your phone's resources are being wasted and how much is being used, please try out either or both of these:
System Tuner, free in the Android Market
SystemPanel Lite, free, paid version tells even more
And if once you're happy, ok to delete those apps if you don't want to bother with more under-the-hood details.
The too-long, didn't read version: App killing is highly overrated and is best avoided 99% of the time.
Hope this helps!