This one:
http://www.hakko.com/english/products/hakko_fx888d.html
You can get it from Amazon, SparkFun, or Adafruit.
It has enough power to apply heat quickly and efficiently, and still maintain tip temperature. Ideally, you want to make the connection as quickly as possible so that heat isn't transferred into surrounding components. I usually solder PCBs at 750F, and haven't had any problems so long as the iron has enough heat capacity. You can easily swap the tips out on the Hakko for fine point work, or something bigger for through hole or large gauge wire. This will be the biggest difference for doing SMD work.
[ninja edit]Skip the hot air rework tools until your proficient at SMD work with the iron. Do some research so you know what a good connection looks like, and what you need to strive for. Once you have some hand on experience, you'll have a much more intuitive grasp of how the heat transfers and what would be easier with a hot air gun. [/ninja edit]