Ah maps.
There are poster maps in the original H, P, E series of adventures from WotC. Some are more reusable than others.
You could try your hand and creating your own with Pymapper:
pymapper | Dungeon Tile Mapping Software
After I export to JPG or PNG format I use Posterazor to make large poster size maps:
PosteRazor - Make your own poster!
The three dungeon tiles box sets are good for making quick and dirty terrain.
If you are OCD like DM Magic check out his campaign on ENWorld here:
http://www.enworld.org/forum/4e-discussion/303354-musings-my-campaign-updated-09-01-a.html
He uses paper 3D terrain from such places as:
Dave's Games
Fat Dragon Games
If you are feeling cartographic and want to build your own maps there is ProFantasy:
ProFantasy Software - map making for fantasy, modern and sci-fi games and for historical cartographers
For old school hex maps:
HexMapper
If you want quick hand drawn and erasable surfaces (wet erase):
Chessex Battle Mats
If you got the dough and find them on ebay I can recommend Tact-Tiles (Out of print, dry erase):
Pics:
http://images.cloud.worthpoint.com/...709/08/1_08e19b991fde2c1c26e6c8acf5bc4fe3.jpg
You can pry my two sets from my cold dead fingers.
If you want to be a cartographer, try these forums:
Cartographers' Guild - The Front Page
These guys and gals are all about the making of maps, plenty of tips and step by steps to bring up your game. The stuff they can do in various paint programs is nothing short of astounding.
I am sure there are many other map resources out there, but these are the ones I have used.