I would recomend Iwata HP-B Plus. It is double action, 0.2mm ultra fine nozzle and needle, especially good for detail work. It has very good price in USA, compared to other countries (www.greatmodels.com , 159 $, while in Europe it is around 240 Euro).
If you chose this airbrush, make sure it has PLUS sign, there is also HP-B without plus. The diference is in the screw you can see at the end of airbrush, with which you can limit the travel of needle. It makes it much easier to use, you don't have to keep you finger stedy, and it is good for making long straight lines. In fact, choose any airbrush with this feature.
