I believe the OP wants CPU usage, not free ram. At least that's what his thread title and post says lol. On the topic of free ram, there's a new tweak that just came out today called N Stats Widget. It puts free ram, free disk space, and upload/download speeds in your notifcation center. Looks pretty clean too.
OP, I am not aware of any tweak that places the CPU usage percentage in the status bar. That's actually a pretty good idea for a tweak. I mean if there's demand for an iMessage typing notification in your status bar, there's gotta be a demand for a constant, live view of CPU usage! I think this is what you're looking for. Even if its not, I'm still glad you started this thread because I'd like this tweak myself. It would be good especially when you want to see what is really churning out CPU cycles. If my phone is constantly showing CPU usage, that means my battery is gonna take a beating. This could be a useful tweak for troubleshooting devices. Right now I use the top command in MobileTerminal. That's a great tool. But I'd also like a "birds-eye" view on CPU%.