After I wrote this reply,
Villains & Vigilantes occurred to me. That game hearkens back to 1979, and the 1982 revised version was just cleaned up and re-released by its creators last year. We had a blast playing it as teenagers, and it is a good buy at present. The print version is $14.95, and the pdf is about half that. Here's a link:
Shop | Monkey House Games
Gamma World is a great one for your club. It is very easy to play, and all the components you need (except dice, pencils & paper) are in the box. I think it would appeal to a younger set of players, too; although we are having a good time playing it as well. It is readily available at big book stores, comic shops and game retailers.
Savage Worlds is one that you definitely should have in your library. It is light on rules, and the core rule book (the explorer's edition) is only $10. Better still, try it for free:
http://www.peginc.com/Downloads/SWEX/TD06.pdf
D&D red box is another you might consider. I don't have it, but a similar box was my gateway into the hobby many years ago. It seems like a good product for your club, too. It also is readily available at big book stores, comic shops and game retailers.
Similarly, the new
D&D board games are self-contained and relatively easy to pick up. Also, tile games like
Zombies are fast & fun. The
B Movie card games from Z-man games are fun and non-collectible. I also have a special like for the
Car Wars card game. It's an updated throwback-very fun.
I also think you can't go wrong with old stand-bys like
Monopoly. I have
Star Wars Monopoly and
Lord of the Rings Monopoly which use a token (Death Star or The One Ring) to move around the board when a 1 is rolled on 1 die. When the token reaches the end of the board, the game ends and the winner is declared by counting up the highest money value. Very fun and faster than the old style game requiring one player to drive the others into bankruptcy.
Along those lines, a set of
Chess and
Checkers is probably a good thing to have around, if even just for show. I would also recommend
Yahtzee, but it may be a little too much like gambling with not enopugh appeal for teenagers.
D&D Minis and
Star Wars Minis are both fun & fast games that are susceptible for 1-shot or more long-term play with the expansion books. But, these are all out of print and may be harder to get now.
My love of RPGs, board & card games tends to run to the simpler ones these days. It's always been that way for me with board & card games, and I have less & less time & energy to devote to RPGs as I age. I think that your club would be well-served with a mix of complexity but leaning to more simple games.
Are you taking donations? Also, have you considered that manufacturers or publishers might donate product?