There's a thread on a mailing list I"m on about helping students have access to old classic games. One interesting suggestion was to get a license with steam as an internet cafe. Another was to get a subscription with GameTap. Both of them have interesting older games. Game Fly subscriptions for the students (like buying a textbook) is another possibility. The conversation turned to lists of games people should be playing.
Here's one list from the Game Career Guide - new, old, Flash, board, card, D&D....an ipmressive list -
And here's a list of games that seem to have been abandoned by their publishers or their publishers have gone out of business. You might not be able to play the games, but you can use the descriptions and images on these lists to get a sense for what the games included and how they looked.
And last but not least by any means is to look for game play videos on youtube and elsewhere on the net. This is especially good for older games that just aren't available anymore (or their consoles aren't available. My students use game play videos now to illustrate the games they're presenting each week rather than bringing in hardware we don't have at school.