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SysInfoPlus

Or you can just use SBSettings, I would think, if it’s like the version on the iPhone.
 
Activity monitor touch

Found this little free app that does just what you wanted and more.
I like being able to see when it's time for a reboot, to free up memory.
 
If you are using SBSettings, There is an option to show free memory in the status bar. IMHO that is the easiest way to monitor Free memory. and who doesnt have SBSettings right?
 
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