How to connect 5V sensors to 3.3V digital input (Due)?
Well if you're not sure of what you're doing, you can always go with level-converters for your sensors (that does not apply to shields though)

Level-converters (sometimes called level-shifters) come in different flavors:


breakout board (the easiest to work with)
IC
DIY circuits with a few components


Some are "one-way": they have pin-pairs with converters 3.3V -> 5V, and other pin-pairs with 5V -> 3.3V conversion; others are bi-directional, i.e. you can use the same pair of pins in 2 directions 3.3V &lt;-> 5V.

There are plenty of these converters, and they are rather cheap; here are just a few examples:


one-way breakout usable with 4 pairs of pins
bi-directional breakout usable with 4 pairs of pins
74HC4050 IC discussed here