Every geek should know about this site. Every Tuesday, two or three apps will be available for only $1.99 for 24 hours. There are some ridiculously amazing deals you can get here. I recommend signing up for their email in the upper right-hand corner so you don't miss any. (You can also choose to subscribe to a weekend email with one more exclusive deal).
In terms of Mac apps, $1.99 is practically free — which is why I've been spending at least $1.99 every Tuesday since the site launched (come to think of it, I should be a bit more hesitant…). And the apps that go on sale are really great and high-class. Some I've even owned already. I would say I would love one for iOS apps, but so many iOS apps are already $1.99 or less.
It's an excellent idea for a site and I'm so glad that it exists.