I am looking for a valve that can be interfaced into a computer.  Let
me explain what it will be used for. It will be connected to some type
of beverage(i.e. Beer, soda).  There will be a program on the computer
that opens the valve for a set period of time to allow a certain
amount of beverage to flow through and then it will close it. I don't
really care how it interfaces with a computer(USB, SERIAL), just so it
works and a program can be easily written to operate the valve.

I don't know of any whole unit that exists for this purpose, but I can
tell you a way to go about accomplishing this task.  First off, you
need a solenoid valve.  One can probably be purchased from
http://www.alliedelec.com.  Second, you need a way to interface this
electronic valve with a computer.  I think the easiest way woud be a
basic stamp (www.parallax.com) This can be used to drive a relay as a
microcontroller can probably not switch enough current to drive a
solenoid.  I'm sure there is also a way to do this using a PIC.  I am
by no means an expert in this field, just thought i'd share my
thoughts.

A basic stamp would be serious over kill, and way to expensive.  I'm
not an expert at this myself, but I was going to design a switch to
turn on my coffee pot from my computer.  you could use the same
technique here.  Since Parallel port pins can be latched into an "on"
or "off" position, you would want to connect a transistor to drive a
relay to provide power the the aformentioned solenoid valve.  When you
output the number 1 to the parallel port, the #1 pin will be set high,
which will trip the relay providing power to the solenoid, opening the
valve.  Then you output 0 to close it again.  I don't know enough
about electrical engineering to give you specific plans, so good luck!

The masters of this are at http://www.barmonkey.net/

Maybe they can give you some insight regarding their cheap prototypes.