Lets's take the iPad as the starting point, as this is often the device that causes erstwhile Windows users to take their first tentative steps away from the Microsoft mothership. Apple's syncronisation solution is based around iCloud. Among other things, it enables mail, calendar and contacts to be syncronised across all Apple-brand devices. To use it, it is necessary to sign-up for a free Apple ID (indeed, you can't really do anything on an Apple device without one). The iCloud software is built-in to the Mac, iPad and iPhone. However, the numbers game means that most new iPad purchasers are likely to have a Windows PC. What now?
The answer is Apple's own iCloud Control Panel for Windows. This free utility adds the necessary support to a Windows PC (Windows 7 or Vista, not XP), providing the link between Outlook and iCloud. It will create a new calendar and set of contacts in Outlook (it should pick up the existing details but worst case you can simply drag existing data across from the old calendar and contacts). Email can be made to sync too; however, this requires you to use your Apple ID address. As most people already have an existing email address they tend not to bother with this bit. Now, any time you make a change to your calendar or contacts on your PC or iPad it will instantly pop-up like magic on the other one about 15 seconds later. You can also login to the iCloud website from any PC and view or change things from there.
But what about your mobile phone? You might have an iPhone, in which case that will automatically sync too. But suppose you've got an Android phone and don't want to change to iPhone? No problem. From the Android Marketplace (or rather, the Play Shop as they call it these days) download two apps called SmoothSync for Cloud Calendar and SmoothSync for Cloud Contacts. These cost about £2 each, but are well worth it. Run each one and create a new account, for which you should give your Apple ID details. These apps will then link the standard Android calendar and contact apps to iCloud, such that they can update each other. One caveat: unlike native Apple stuff, the SmoothSync apps do not 'push' the changes automatically. Rather, it is necessary to explicitly sync the changes. In theory you can configure them to do this on a regular basis, say every 15 minutes or so. In practice, this may not work due to inconsistencies in setting up general background sync on some Android phones. However, forcing a manual sync once or twice a day is not exactly a hardship. Another consideration is that new calendar and contacts files are created on the phone (much as happens when the iCloud Control panel is installed on a PC), so it is important to use the right ones on the phone or set the iCloud ones as default if that is an option. Other than that, it works a treat.