Taxis in Cancun are easy to obtain no matter where you are.  They are lined up anywhere a tourist may be.  Taxi prices are standard - there is no bartering necessary nor is it welcomed.  The best thing to do is to ask the concierge or front desk in your hotel what the standard taxi rates are.  Many times hotels even post the rates because they are standard througout.  For example, when we stay at the Moon Palace, there is a standard rate to anywhere in the hotel zone - it doesn’t matter if you are going somewhere south in the zone or at the top of the zone, or how long it takes to get there - the rate is the same.

Taxis take both types of currency, but it is best to pay in local currency so you don’t have to worry whether you are getting correct change.  Often if you pay in American dollars, your change will be in pesos.  If you are good at math in your head, you could figure it out, but we don’t care to so we always pay in pesos. 

Buses:

It's very inexpensive (about US$0.50) and convenient to get around Cancun by bus. Not all buses are airconditioned.  Driver will make change.

Taxis:

Within, to and from the hotel zone, it can be very expensive.  Always ask how much you will be charged before the taxi trip starts.  You can negotiate the price, make a counter-offer.

From the airport to anywhere: exclusive-taxis charge non-negotiable US$40.00 or MX$400.00 (pay in any of the taxi stands inside the airport).  You can take a collective taxi ("colectivo") for much less, you just have to travel with other passengers, and do a small milk run.  From anywhere to airport: feel free to negotiate, but expect about MXP$200.00 pesos.

Downtown cancun: cheap.  Make belive you are a local, don't let the taxi drivers screw you over.

Taxis will not issue receipts, except if you buy within the airport taxi stand.

Rent-a-Cars:

Its better to rent a car or a scooter if you plan to move around a lot, its cheaper than taxis.  Parking is a pain in the hotel zone.  When you buy gas, keep in mind that Mexican gas stations tend to overcharge (or undeliver) gas, i.e.: they tinker with the meter and charge you 10% more liters than whats actually delivered.

Bicycles, roller skates: in the hotel zone, there are some strips were you wont have any problem, but around "Punta Cancun" (northeastern point of the hotel zone) you can forget about it.  The same applies for kid-strollers.

Walking: sure, why not....