If yoy want a cheap, but good, gun to start with, I recommend a brand called Jing Gong. They are basically Chinese copies of Tokyo Marui (which again is one of the biggest airsoft suppliers).
If you want good and solid, Classic Army is very good. They come standard with a muzzle velocity of 350 feet per sec., and metal body.
Last, but not least, Tokyo Marui is launching a new M4. Which includes metal body, recoil system, bolt stopper (stops when your out of ammo in the mag, and you have to operate the bolt catch release).
See more of that, here: http://hk.youtube.com/watch?v=xIO7SCrYcuA
Good luck!