Tables on Apple’s support site show you what types of purchases you can download again in each country and in which countries iTunes Match is available. If music, apps, or books are available in your country, you can enable Automatic Downloads on your computers and iOS devices to automatically download new purchases made from other devices.
The iTunes in the Cloud and iTunes Match Availability tables are here.
[Attribution: GigaOM. Thanks to MacDailyNews Reader "Fred Mertz" for the heads up.]