So I came upon an app the other day while browsing on my iPhone. iStat. It monitors your uptime, network I/O, RAM usage, etc.. There was another app that just needed SSH access but that was another $2. Anyways, iStat has a Mac OS X, Linux, FreeBSD and Solaris port of the agent. Just simply install the agent on your boxen and done!
It's pretty simple to get it working, I'll go over the steps that I used on Lenny.