Check with your state regs but, as mentioned, they are legal in the majority of states.

May I suggest a Barrett M82A1: http://www.barrettrifles.com/rifles/rifles_82A1.htm or a Barrett M95: http://www.barrettrifles.com/rifles/rifles_95.htm. If you're wanting something a little more economical how about a Barrett M99: http://www.barrettrifles.com/rifles/rifles_99.htm. Oh the choices!