It depends on what you consider a true ghost towns. Most of the places mentioned by posters above are still active and inhabited towns that have significant year-round populations and businesses and are now popular tourist attractions and artist/retiree communities. Arizona also has many true ghost towns (over 200) that have few or no people living in them, but be warned, most of them are not like what you see in the movies and TV with rows of buildings still standing. The best ones might have a few standing buildings, but most have no more than a few faint foundations and some scattered pieces of trash and rubble (they are still very interesting, but you have to know what you are looking for and what you are looking at).
Here are my picks for the best Semi-Ghosts and True Ghost towns in Arizona:
Jerome (along 89A north of Camp Verde) - Old copper mining town that was major city during turn of the last century and still has many impressive historic buildings from that period all situationed on a steep mountain slope. Many cafes, B&Bs, shops and art galleries now. Be sure to visit the Douglas Mansion museum.
Oatman (along old Route 66 near CA border west of Kingman) - Gold mining town that hit its peak before WW2. Single main street with historic buildings (now holding tourist shops). Famous for the semi-wild burros that still wander the streets (left over from mining days). Scenes from 'How the West was Won' were filmed here.
Chloride (North of Kingman toward Las Vegas) - Another old gold mining town - kinda a small version of Oatman. Nearby is the 'painted cliff of Chloride' where a local artist painted a mural on a cliff side.
Bisbee (south of Tombstone in Southern Arizona) - Like a Jerome, this was a major copper mining town built on steep mountain slopes with many historic buildings now filled with cafes, galleries, shops and B&Bs. You can take an underground mine tour at the nearby Copper Queen Mine.
Clifton (North of Safford in SE Arizona) - Probably the most abandoned and 'ghostly' of the semi-ghost towns. Chase Creek street (the original main street) has 2 full blocks of mostly abandoned buildings - some of them quite impressive and ornate.
Note that while all of the above have interesting historic buildings and are no longer as big as they used to be, NONE of them are true completely abandoned ghost towns and all of them have permanent businesses and populations (Jerome and Bisbee have fairly large populations).
TRUE GHOST TOWNS
The following are my picks for the best true ghost towns that are nearly or completely abandoned:
Sasco (west of Red Rock, near Picacho Peak north of Tucson) - Copper smelter town from the early part of the 20th century (processed the copper ore from the Silverbell mines). Extensive concrete foundations of the smelter, power plant and railway buildings, standing ruins of the jail, hotel and company office plus many foundations. This where my Yahoo name is from.
Vulture Mine (west of Wickenburg) - One of the largest gold mines in the state and still has about a dozen standing buildings, some with furniture and equipment still inside. A caretaker charges a small admission fee to wander around (which is why it is so well preserved).
Swansea (out in the desert east of Parker) - Completely abandoned copper mining town from the 1920s. Many roofless ruins including a row of miners cabins, the company store, railway depot and major ruins of the smelter. Tough to reach.
Charleston (along San Pedro River east of Tombstone) - Rowdy cowboy and mining town during the boom days of Tombstone in the 1870s and 1880s. Now overgrown by brush and mesquite trees, but there is still a row of probably over a dozen adobe shells (in various states) indicating where varies streets, etc were. It is on the west bank of the San Pedro river just north of the road from Tombstone to Sierra Vista.
Contrary to what a poster above states, there are very few ghost towns (let alone good ones) near the Grand Canyon. Flagstaff and Williams are both large thriving towns with populations in the thousands and probably larger today than they ever have been. They do have interesting historic buildings, but they are not and never have been, ghost towns.
Arizona resident and historian. Have published articles on Arizona's mining history and have visited most of the major ghost towns in the state.
For an excellent guide to Arizona's ghost towns, see the book "Arizona Ghost Towns and Mining Camps" by Philip Varney
The following website has a comprehensive listing of ghost towns with descriptions and brief histories. Be warned that some of the historical and descriptive information on this site is often inaccurate: