When you have users who rate stuff, they have been taught by Amazon to expect recomendations. For this the most common used way of generating recomendations is done by collaborative filtering.
A great demonstration on this is done by MovieLens and this is build on the theory located here.
If you are using Drupal CMS, there is a module for making recomandations. Another PHP/MySQL system is CoFIND where you also can download the source code.
I will try to test it - perhaps on my recipies, which around 40 unique users is accessing each day.