All of the e-cigarettes are made by a handful of Chinese companies so make sure you know what you are buying and whether or not it is a respected model. In general, anyplace that charges more than $10 for an atty or more than $15 for a battery is a jacked up rebrander.
Check the sticky threads at the top of this New Members section, especially the newbie videos and the thread with Library in its title (that leads to a great multipart illustrated guide). Both will discuss most if not all of the most popular models.