One of the better resources I have found if you are looking to purchase a new or used Mazda is Smart Car Guide. For specific model information and pricing look to Edmunds and for reviews try Consumer Reports.

Hundreds of Used Mazda's can be found at Auto Trader. Also worth checking out if you are looking at used vehicles and want to review recalls and service bulletins, try All Data. For a reasonable fee, CarFax will check a vehicle's history for hidden problems such as an odometer rollback or salvage damage.