The Field Museum has an impressive online exhibit on Maps of the World. It combines a world map with a timeline, and you can see various versions of maps from different periods and of different parts of the world.
The museum also has a section called All About Maps, which is a guided tour through the exhibit.
I’ve placed both links on my Geography page under Introduction To Maps.
In addition, as part of the online exhibit, you can send an eCard of a map with a message and then post its url on a website or blog.
I’ve placed that link on my Examples of Student Work page under eCards.