BlueWater Ropes Rappel Rack
Price Paid: somewhere around $40 (a while ago)
For other than recreational mountaineering, this has been my preferred rappel system for many years, especially on long drops. I like the great amount of control available, the degree to which you can rappel just a little tint bit, and the ability to lock off positively.
I have used it for mountain rescue applications, and also for applications doing archaeology and paleontology where rappelling was necessary to reach sites and specimens. The longest of these was a situation calling for a 580' rappel, most of which was free. On that occasion, a hot summer day, it was necessary to carry a small water bottle to cool down the rig which did get a bit hot. I think I have always used a six bar rig.
The rig is a bit bulky, but for the situations that require a rack, that is a highly acceptable tradeoff.