Geolocation seems to be quite popular at the moment, which gave me the idea for this entry to the Plugin Competition.

Content By Country (CBC) enables a blogger to target post content by a user’s IP location, using [cbc][/cbc] tags. Post text can be included or excluded from view for one or more countries at once.

eg. [cbc:+usa:+ca]Text goes here[/cbc]

The example above would only show the text to visitors from the USA or Canada

Download / get more information here