I've been looking for an online copy of a map of the early Salt Lake City wards, so I was interested to read my father's post yesterday on his genealogy blog (Update of Maps Online).
I didn't find the map I was looking for, but what marvelous resources he lists! The most useful one I've seen so far is the David Rumsey Map Collection which includes the MapRank Search.
I enjoyed this map of Rhode Island, since I visited the state recently. (Very briefly!)
For other map resources, see the post at Genealogy's Star (Update of Maps Online).