This research guide shows various online sources for images of maps. You can download maps from these resources. If you want to actually map data online, please see Mapping Online.
If you have any suggestions for resources, let me know.
If you're looking for good, accurate base maps you can in presentations and papers, here are a couple of sites for you to use:
"The Nations Online Project - is, among other things, a more or less objective guide to the world, a statement for the peaceful, nonviolent coexistence of nations. A statement in favor of cultural diversity and the free flow of information and knowledge across national, cultural and religious boundaries."