Right now I have 546 being used and 278 free. I rebooted my phone 3 days ago. You always have more RAM after a reboot it seems like. You can increase your free RAM by disabling or uninstalling apps you don't need. Some of them keep turning themselves back on after you stop them. This is eating up some RAM. Not much, but some.
reboot once a day. facebook is a big ram hog and so are any widgets. any apps you don't check often you can disable push notifications. The only major improvement is gonna come from looking at your list of running apps and uninstalling the ones using the most ram. i really think the task killer apps are counter productive and cause problems