I'm constantly beset by the need to reach a computer that's not within reach: a server located 15 miles to the south, a laptop at home, or a "headless" system (no monitor attached). LogMeIn is one of the tools I rely on to complement Timbuktu Pro and Back to My Mac's screen sharing. LogMeIn's Mac OS X version, a free screen-sharing utility, lets me manipulate my computers remotely, even those inside my ostensibly locked-away home network.
The company has now announced a limited beta test of LogMeIn Ignition, an extension of their system, which relies on client software and centrally coordinating servers that they run, to the iPod touch and iPhone.
The App Store currently offers some remote-access packages, although these rely on VNC. VNC is built into Tiger and Leopard, but it requires directly reachable IP addresses, whether you use port mapping or have a public IP address on the computer you want to connect to. LogMeIn can traverse NAT and other obstacles to end-to-end connectivity.