Transistor switch logic, multiple lines
Here is a 600 ma / 1 a   ic.
Dual H-Bridge Motor Driver for DC or Steppers - 600ma - L293D

$2.50 from adafruit  even cheaper from china [ $.50 ]

see data sheet at  http://www.adafruit.com/datasheets/l293d.pdf

L293   1 amp  requires external clamp diodes.
L293d  600 ma  has internal clamp diodes.

I use one of these, to run 2 12v dc motors,  n gage model trains. 
pulse 1 side of bridge for fwd, and other for reverse.
both hi will cause both outputs hi,  no problem, 
  no voltage differential therefore no current.
i use arduino pwm to controll speed.