After having glued together my last kits together at least 15 years ago as a kid I was surprised with the Revell 1/48 B-25 I got last christmas. Since this is the type my grandfather served with I decided I really wanted to do my best with it. So I bought some paint, borrowed an airbrush from a friend & had a go at it.
I must say the results, even for a first time user like me, are something I could never hope to archieve with a brush. If you decide to get one, the really basic starter sets are a waste of money. These are usually single-action, which means they are basically spraycans where you put in your own paint. The double-action models give you seperate control over the airflow, and the paintflow. A basic compressor will do (piston preferrable over membrane), but you can upgrade those to a model with a small air tank. I would suggest a combined moisturetrap/pressurevalve & meter to go with that.
As for paints, you can use about any sort of paint, but cleaning the airbrush can be a hassle sometimes. If you use enamels you have to clean with paint thinner, and those can eat away the O-rings and gaskets. Personally I only use waterbased acrylics like Vallejo now. You'll only need water to clean it. Tamiya acrylics are very good too but are alcohol based, and as such need to be thinned with 90% alcohol. The fumes are toxic too.
In all, for about 120 quid you should be able to get a decent set that will serve you for years to come. Some specialised vendors sell their own brand of airbrushes, which are usually perfect as startersets. They might also have used ones. Unless you already know you will pick up modelling hardcore there is no need to spend some serious cash on the high-end brushes. The one I use now is a Premiair G35, but pretty soon I'll have to go look for my own set too...