The best I have found that are easily obtainable and pretty easy to set up are the DETOLF glass cases from Ikea. weighing in at about 60lbs and at a cost of about $60 each, with measurements of 16 w x 16 deep x 63 inches tall, these are the best glass cases for the money. There are vastly more expensive and larger glass cases out there and you are most likely going to find them on eBay. Go to YOUTUBE and Check out Hot Toys collector Cheskadudu under "Hot Toys Glass Display January 2011", for what I would consider the ultimate glass case that he purchased off of eBay for $475...I plan on adding one of these to my display cabinets.
Also from Ikea is their LACK shelves, these bad boys are 77 inch tall and 41 in wide x 15 inch deep, with a gloss black exterior...these ran about $250 each, but worth every penny.
I've tried other types of bookcases and they just buckle and warp from the weight, which in turn makes them look every bit as cheap as they are. for my money its Ikea all the way, until somebody comes along with something comparable in styling and price point!
Almost forgot to mention, I use plastic spice racks from Bed, Bath and Beyond, so I can get some height difference when displaying action figures. They carry one large ($7.95) and one small ($4.95), and one expanding ($10.95), that pulls apart in the middle making it longer.
Here's a couple of pics of the shelves and cabinets...
