Hard drives can get pretty hot. The drives in my dad's PC exceeded 60C - there were three of them, each 7200rpm drives, crammed right close together in the 3.5" internal bays. There still were no problems with them, but I moved two of them to the 5.25" bays using some cheap metal adapters. There's still no airflow over them, but at least there is open space, which has helped bring their temperatures down.
I like the cases that have a hard drive cage set right in front of an intake fan. My case is an Antec SLK3700AMB - 5-drive cage directly in front of a 120mm intake fan.