The L293D (600mA max) has got a high voltage drop (up to 3.6V), so you may end up with as little as 5.4V for the motors (with a fresh battery).
Try the FAN8200 series (Fairchild) instead, if the current is below 650mA. It comes in four variants:
FAN8200 = 650mA max.
FAN8200MTC = 550mA max.
FAN8200D = 400mA max.
FAN8200MP = 350mA max.
(Each will drive 2 separate DC motors)
If your motors need more current, you need something else of course, but there's so many motor driver chips that it wold be pointless mentioning any without knowing the current your motor takes when loaded.