Well, if your looking for something with a true "artistic" style, you can't beat :Koppollex: A medieval town map tutorial in Photoshop and Eneini: a medieval city tutorial (in Photoshop), both by Pyrandon for making City maps in Photoshop.
There are tons of other tutorials here by many authors which provide many different styles of maps for you to pick and choose from. As you map, be sure to post up your works in progress and we will be more than happy to provide constructive criticism to help you get where you want to go.
Joe