We typically put the amps at the bottom for stability and becuase heat rises. So they will naturally vent. We will do 1U vented blanks between amps and major heat sources (receivers). Sometimes DVR's and cable boxes too (these puppies can get hot). We put DVD players and any other device you have to load often at a natural height so they are easy to reach and see what you are doing.
The environment the rack is going in will determine what if any ventilation we are doing. Big open air basement that is typically cool might not need any fans. Anything that is going to be enclosed in furniture or a closet will need something. But again it depends on the size of the closet. We just did two racks side by side and didn't have any fans installed but the closet was a decent size and since we were involved when the house was being built so we were able to have the A/C guy put a vent in. The room runs at the perfect temp.
