Ive been a fan of AC Infinity! Pun intended.
For my AVR I use an Aircom T10 ((?) front venting unit with digital display and additional ports for controlling extra fans). They also sell smaller units and fans only... wide range of gear. And I think the T8 model is rear venting which is ideal if the back of your cabinet is open.
Depending on your cabinet, you can also just rig up your own series of ultra--quiet PC cooling fans.
Also important is most of the manufacturers recommend 6-8" around all sides and top for proper ventilation.