So I've been reading a few threads here and on other forums. I understand there are various solutions for stepping down or up a voltage. What I have found are the LVC series shift regs that give a constant ouput, MCP1825 which will step down 5 to 3.3 (and other versions which have different increments) the 74LCX245 which will step 2.5 or 3.3 to 5v and perhaps some others I am forgetting. Then there are ready made boards such as the Sparkfun converters or this 8 pin to 8 pin converter. But all of these are one direction only, or bi-direction switched by a jumper.
How would I convert voltages down or up in both directions without requiring a pin select.
Sparkfun has a tutorial on sensor interfacing/logic-level conversion that might be useful to you.