GOG.com has launched a huge summer sale today, with over 500 games available for very cheap and more changing in and out every day. I'm mentioning it here because the site has a big Mac section with classic games like Dungeon Keeper, Syndicate and even the great System Shock 2 all on sale for less than US$5 each. Alpha Centauri is one of my favorite games ever, and it's also on sale, as is the recent indie success FTL: Faster Than Light.
GOG is even offering the excellent dungeon crawler Torchlight for the low, low price of completely free, so definitely grab that and play it if you haven't yet. The big sale lasts through July 5, and there will be more titles in the mix as the event goes on, so stay tuned for more great games to play on your Mac this summer.