Here's a site that hosts some historical maps of SL. It's amazing to see how small the grid was waaaay back when (2002!)

You can find various assorted maps and map tools at this site. It also has a cool feature: snapshots of the mainland areas (by name, not feature, though) from any day in SL's history.

http://www.slmaps.com/
(Use the form near the bottom of the main page of the site to enter your own dates to view).

For example, to see what the grid looked like on Monday, Feb 26, 2007:

http://www.slmaps.com/dategrid2.php?css=grid.css&date=2007-02-26

I found this mostly helpful because now I can do a search for the name of a sim, and easily see the other sim names around it. Even though I can't see what's there, it gives yet another filter thru which to view things.