Check out www.airsoftextreme.com
I purchased a G18c. I use for Ipsc practice, shooting courses of fire in the garage.
Stay away from the spring or electric versions, its the gas blow backs that are closer to the real thing.
Shooting airsoft has helped me with shooting on the move and site picture.
But it has its limits. Even with the modifications I have done to my G22 (the real one) the airsoft gun has a lighter trigger pull than the G22 I shoot IPSC.
I try not to get to dependent on the Airsoft for that reason.
Its still alot of fun.