Voltage translation app note from Fairchild Semiconductors, this app note include their auto bi-directional voltage translator that removes the burden of direction control. Link here (PDF)
Voltage translators, or “level shifters” as they are sometimes called, allow the coupling of signals that do not share common VCC domains. For example, a signal generated from a 1.0 V device may need to connect to a 3.3 V device.