The Internet Arcade is a web-based library of arcade (coin-operated) video games from the 1970s through to the 1990s, emulated in JSMAME, part of the JSMESS software package. Containing hundreds of games ranging through many different genres and styles, the Arcade provides research, comparison, and entertainment in the realm of the Video Game Arcade.
The kind and fantabulously generous Sir Awesome of Touch Arcade has compiled a huge list of games that have had their prices slashed this holiday season. If you're after more of a 'curated' list, with actual links to iTunes, they have a blog post up with their list of must-have discounted games.
Most games on the list seem to have undergone massive, more-than-50% discounts.