Chiang Mai is relatively easy to get around, since it's a very tourist oriented town. While there are now licensed taxis, they seem very hard to find on the street. They seem to all hang out at the airport. You will find a few men with cars hanging around outside many hotels offering to take you on tours, etc. Use them at your own risk. Here are your other options for getting around:

Tuk-tuk

These three wheeled carts, properly called a samlor but universally referred to as tuk-tuks, are generally the quickest way to get somewhere. Chiang Mai is small enough that the tuk-tuk appropriate for getting around town. Note that despite their noise samlors don't have a lot of power so you won't find them climing the hills outside of town. Be sure to negotiate the fare before starting your trip.

Songtaew

These are small pickups fitted with benches along the side of the bed. They operate like buses, picking up and dropping off passengers as they go along, except that they have no fixed route. You need to flag one down and find out if where you want to go is on his way before boarding in the back. Songtaews are also the common form of transportation up to Doi Suthep and Doi Pui mountains. You'll find Sontaews going up the mountains around the night bazaar area as well as just outside of Chang Puek gate.

Motorcycle

You can rent morotcylces from several places around town, and they make a great way to get around, if you're able to ride. Note that helmets are required.

Car

There are a number of car rental agencies around town, including some of the international chains such as Budget, Avis and National. Driving in Chiang Mai is not as difficult as Bangkok, but you'd still be well advised to rent a car with driver.

Airport Transfers

The airport is extremely close to town, and it's generally no more than a 15 minute drive to most city hotels from the airport. Many, if not all, hotels offer a pick up service, but check the charges before you order hotel transportation. See the Chiang Mai airport transfers page for more details.