Pronounced Ribati-, Liberty is a chain of stores, mostly in Akihabara, although there are some in Shinjuku as well now, that trade in used media. IMHO, the cheapest prices for DVD's, console games, laserdicss, etc. are to be found by browsing through the different Liberty stores. They usually don't set prices amongst each other, but the cheapest deal is mostly offered by one of the Liberty stores. They have well sorted Anime, movie, music, game, and (of course, being Akihabara), porn sections. Although they also have some new product, they usually give you a flat 15 % off the suggested retail price, a very good deal in Japan.
If I found them all, there are two Liberties in Shinjuku, although their prices are the highest of the lot, and 5 in Akihabara. If there is others, I never saw them. Two of them are right next to each other on Chuo-dori, usually called the Two Towers as they are in two larger buildings, each on one side of a small side street. There also is the big Liberty, just a bit off Chuo-dori. These three are the most important and have the most and cheapest wares, but sometimes, a "pearl" is to be found in the smaller ones as well.
BTW: if you buy something used here in Japan, you can expect it to be of top quality, complete with all extras. Somehow, used seems to mean: used just once, then stored in a time vault, until being resold at ridiculary low prices to the used goods stores.