I've found Cover Flow to be really cool while I'm browsing files. However, I notice that the more files I browse, my RAM usage in iStat Pro slowly starts to climb, and doesn't seem to go away after I close the Finder. Is there some way to "clear" the RAMm so it isn't using up my memory?
Try quitting and relaunching Finder. Just go into the Apple menu, click Force Quit..., click on Finder, and then click Relaunch.
Don't worry about the RAM being used up, that's what it's there for. If you go into Activity Monitor and notice that for some strange reason that your "wired" ram is taking up almost all of your memory, then try a restart. But pretty much OS X is smart enough to replace the items in your memory with new items that you need quick access to. I've read about people being worried about iTunes using all of their RAM. Well, if you have 2-4gb of RAM and iTunes wants to use 300mb to keep track of album covers while you browse the internet, let it. When you decide to open up Photoshop and do some work, if Photoshop needs the RAM for anything the OS will hand it over.