The first generation Grand Cherokee ZJ was an upgrade of the related Cherokee. It was supposed to be a replacement for that vehicle in 1993, but Cherokee sales were too high to cancel it. First generation engines ranged from an I6 to a V8. Only 4 speed automatic transmission was offered. The trim lines included Base (also called SE), Laredo, and Limited.
The second generation Grand Cherokee WJ had a stiffer structure thanks to Porsche engineering. The vehicle was made lighter and more powerful than the ZJ. Some of the special models include the Sport, Special Edition, Overland, and Columbia Edition. I think the final one there came with several kilos of pure Columbian "snow" in the back.
The WK model has been made since 2005. It has Quadra Drive II four wheel drive and a DVD player in the rear seats. The SRT-8 is a new model introduced for this generation.
These Grand Cherokees can be found in just about any used car listing, including your local paper. You'll find plenty of parts from all generations on places like eBay.