There is still much to learn about task management and whether Android itself does a good job managing tasks/services. But sometimes, I wish I could kill a specific task, just to free up memory or stop data from being consumed.
Advanced Task Killer (ATK) is a Froyo-specific app that somehow bypasses Android and allows you to manage tasks yourself. The interface still needs some polishing, but the app works as advertised. When you open it, you will see all tasks running at that moment. Check marks indicate which tasks you are about to kill, and give you the option to exclude some.
If there are specific apps you always want to keep running, the settings menu offers the option to create an ignore list. By default, ATK will launch when you boot your phone and add an icon in the notification bar, giving you easy access. These settings can, however, be overwritten.
You can also kill tasks by using the supplied widget. ATK will place an icon on one of your home screens and by tapping that, you can kill all running apps at that moment (except those that are in the ignore list, of course).
As the app is free, I recommend you give it a try, and see whether your phone gets quicker and consumes less battery power after using it. You don't have to be very tech savvy to understand ATK, but if you're fine with Android managing your tasks (and worried about potentially breaking things), there's no real need to install this app.