Android/Windows Mobile/BlackBerry: Nowadays, a lot of us store our whole lives on our smartphones. If your phone gets lost or stolen, free web service Lookout can back it up, locate it and wipe it all from a web interface.
If you keep valuable or sensitive information on your phone, it's nice to have a plan in case it gets lost or stolen, and Lookout can help you manage your data if that ever happens. Even if you don't have sensitive information on your phone, though, Lookout can still be useful — just like on your PC, antivirus and backups are always important in case anything happens.
You'll need to download a quick app to your phone, which gives Lookout access to it (as well as displays the status of your backup and anti-virus on the go). Most of your work with Lookout will be done on your computer, though, from Lookout's web interface. From any browser you have access to all of Lookout's features: you can back up your phone, find it if it's lost, wipe your data and run virus scans remotely. It's super easy, requires very little set-up, and is an invaluable safety net if and when your phone falls into the wrong hands.
Currently, Lookout works with Android, Windows Mobile and BlackBerry devices, although an iPhone version is also planned for the future.