Crazily, Microsoft has removed the excellent Windows Media Center from Windows 8, quoting codec licensing costs as the main reason. It does, however, sell a separate Media Center Pack for Windows 8 Pro that costs £6.99 (Windows 8 standard version needs to be upgraded with the Windows 8 Pro Pack costing £49.99 at the time of writing).
Those already running Windows 8 Pro don't need to pay a penny, as Microsoft is offering free upgrade keys to anyone until 31 January, 2013. Just go to http://windows.microsoft.com/en-GB/windows-8/feature-packs and enter your email address. There are no limits, apart from one key per email address. Once the key is received, it can be added to Windows using the Add Features to Windows 8 tool (just search for this from the Start screen, and it appears in the Settings results). Click 'I already have a product key' and enter the key. The upgrade will take place, and Media Center will be available after the restart. It is unchanged from the Windows 7 version, and still works with up to three analogue or digital TV tuners.