You may also consider looking for newer versions of your sensors. You may be able to acquire sensors that both work with the same voltage limits, or you may find out that newer versions of the sensors are available which will give you digital outputs and can be polled with I2C or other simple serial communication protocols. It would require buying a new chip, of course, but they're not terribly expensive and not only would you eliminate the problem, but you would likely provide your project with a greater level of precision since you don't have to worry about noise in your circuit.
Short of redesigning your entire project to fit new chips, John C and the ham provide excellent, simple solutions. In my experience, I have run a 3v3 sensor with a 5v supply and reference and have had larger issues with noise than with lost resolution for casual projects. This is the easiest way out, but does require you to do some math, and I have voted ka1kjz's post up accordingly (do check the reference sheets).
As far as the voltage divider solution goes, as long as you use higher-precision resistors you get the advantage of having all of your measurements be in the same voltage range and you get the ratiometric correction benefit of using AREF to follow any voltage ripple. In practice, however, I've found that noise and lack of calibration techniques in my projects have contributed more error than a little voltage ripple or 10% resistors could reasonably cause. For that reason I have voted JohnC's solution up as well, since he covers all this in more detail.