Off Remote, an iOS app from Hobbyist Software could be handy addition to your home automator's toolkit. By installing a simple server component on your Mac or Windows computer, you can then use your iPhone to turn the computer off, put it sleep, restart it, and so on. It's especially nice that it works on Macs and PCs. Off Remote might be just the app you need when a VNC-style approach is overkill.

See the Macworld review by Glenn Fleishman too.