iStat, it easily frees memory plus allows you to see information about how your iPhone (or mac) are running.
iStat +1. Having access to your main computer is nice too, and it does other stuff (e.g., ping). But if you want a really cheap & easy way, just restart your device. That clears the memory out just fine, except it takes a little while.
Add another vote for iStat. But, if you want the desktop readings, it may be mac oriented. I am not sure because I am just so mac oriented. I do know it is on sale right now.