iPhone/iPod touch only: Free online sharing service Soonr has launched an iPhone/desktop app combo that gives you 500MB of space to keep your Windows or Mac documents synced to your device. After signing up at Soonr's site, installing the desktop software from an emailed link, and installing the free iPhone app, you're pretty much on your way. Soonr's "Desktop Agent" software lets you choose what folders or types of files get synchronised to your device and how much bandwidth gets used doing it. Soonr's app lets you preview Microsoft Office, PDF, text, and image files, and even lets you print to networked printers if your iPhone/touch is connected to a Wi-Fi network. Check out screenshots of Soonr's desktop application (on Windows XP) and iPhone capabilities below:
Soonr is a free download and sign-up, requires a PC or Mac computer and an iPhone or iPod touch. Looking for a less cloud-based, controllable solution? Try the previously mentioned (and previously free) Air Sharing.