http://www.airsoftcanada.com/showthr...ht=battery+faq
There is quite a bit about Ni-Cd cells and how to discharge them properly.
As for what to use to properly discharge a cell. Most high end chargers have a variable discharge setting, I assume this is the best option. I have also seen other products like the TM discharger on the battery page from 007 airsoft, not sure how this would work compared to a charger.
http://www.007airsoft.com/products/htm/consumables.htm