Microsoft's SkyDrive offers remote access to all your Windows PCs, including attached external drives, that have the SkyDrive desktop client. During installation of the desktop client, you will be asked to authorize remote access. After the client is installed, log in to skydrive.com on a Web browser from another computer.

In the left column, you will see a 'Computers' section listing all the Windows PCs connected to your SkyDrive account. Select the computer you want, and then SkyDrive may ask you to enter a six-digit code sent via email to authorize remote access. (The authorization code will not go to your Hotmail account, but to your alternate email address that Windows Live has on file.) After you enter the authorization code, you can access your PC's file system via the SkyDrive Web interface. To use this feature on a mobile device such as the iPad, you will have to enable the PC version of the site at the bottom of the Web page.

If SkyDrive doesn't interest you, SugarSync provides similar remote-sync capabilities for Windows and Mac.

A beta service called URL Droplet lets you send documents (such as PDFs and spreadsheets) found on Web pages directly to your Dropbox, no manual download necessary. Simply and authorize the service to access your Dropbox; URL Droplet uses the Dropbox API, which means the service never sees your account password. Next, paste a link to the online document, and click Save. The file will appear in Dropbox and sync across all your devices.