Now if you want something to monitor your apps, personally I'd suggest Watchdog. Instead of monitoring memory usage, which is irrelevant and useless information, it monitors CPU usage then warns the user when the program hits a predefined threshold of background CPU usage.…What people don’t seem to realize is that android is designed to have a large number of tasks stored in memory at all times. Why? Well basically we are talking about a mobile device. On a mobile device things tend to be slower. The hardware isn’t as robust as say a desktop or a laptop, so in order to get that same “snappy” feeling, there have to be workarounds.
One of these is how android deals with memory. Android will load up your apps and then keep them running until they absolutely HAVE to kill them. This is because that way, if you want to re-open an app, the system already has it loaded and can then just resume it instead of reloading it. This provides a significant performance increase.