Since I re-started my D&D habit last year with the release of 4th Edition, I've been playing pretty regularly with a very entertaining bunch. One online tool I've found very useful has been Obsidian Portal. It's a great website that allows DMs and players to manage their campaigns and characters. You can add characters, images, game logs, NPCs and maps. There is also a Wiki for your campaign.
I think my fave feature is the google maps application layered over the maps you add. You can then add pins to locations with links to their wiki page. Sweet!