You've got just about 18 hours to get in on GOG.com's latest sale, which includes a number of EA and Telltale hit games like Dragon Age: Origins, Crysis, Dead Space, Mirror's Edge, a number of Sim City, Medal of Honor, and Wing Commander titles, as well as Batman: The Telltale Series, and Telltale's The Walking Dead all for up to 80% off individually or for a bulk 75% your selection of sale titles.
Most of them are windows only, but there are a number that have mac support, and with GOG or their GOG Galaxy client, you've got them DRM free. You can check out the GOG sale here while it lasts.
Humblebundle's weekend sale is a pay what you want tinyBuild bundle which includes titles like The Final Station, Divide by Sheep, Guts and Glory, and more from the small indie developer. You can check out that full sale here.
Humblebundle's also got a very positive pay what you want sale which includes a number of indie titles like Super Mega Baseball: Extra Innings, They Bleed Pixels, The Deadly Tower of Monsters, and Hacknet. You can take a look at that sale here.
Because nothing says "I appreciate you mom" like video games, these sales all expire at the end of the weekend.