.

Well, with the sale in mind...

• Bit.Trip Beat
• B.T Core
• B.T Void
• B.T Fate
• Super Hexagon

Two 4-packs of Super Hexagon, or 3 copies of Super Hexagon if you already own it. I gifted 8 copies of Super Hexagon to friends over the course of the sale using money from snow globes and trading cards, it's a cheap and immensely entertaining game, the more friends you have to compete against, the more fun it is.

A few tables for Pinball FX2, Half-Life 2, GTA Vice City, Trine...

• Duke Nukem: Manhattan Project
  aaaand that's about it.

Really Big Sky. A randomly procedural generated Shoot-em-up.
Toki Toki a clever puzzle platformer.
Defy Gravity Extended, an action platformer where you control gravity in a classic style ide-scroller.
Fortix and Fortix 2. Qix inspired game where you "paint" an area to capture it and it's a matter of mastering how much you can/should grab with risk/reward. Simple to understand, fun to master.
Lunar Pack, containing the exploration platformer title Lunnye Diversity with the "Metroidvania" like Wake which is set on a sinking ship and backtracking is fun.
Sequence. A RPG with a DDR inspired battle systems (using keyboard or game pad). Also playable with DDR mat for PC if you can find it and don't mind extra hassle.
Dark Void Zero. A NES inspired action game where you find an item before moving on to the next. Notable for being a promotional game that ended up better than the AAA game it was created to promote. Not recommended if you don't actually like old NES/Master System like games where you have to find an item, back track, and is full of respawning enemies.
Numerous SEGA Mega Drive/Genesis games like Shadow Dancer and Shinobi III.
Ultraton, a classic style twin-stick shooter closer to Robotron than Geometry Wars.
Critter Crunch, a pick and drag match 3 or more puzzle game with interesting game mechanics. Overly cute.

Wait for Binding of Isaac and its addon to be 75% off or less.

Fortix + secret of the magic crystals or fortix 2.

But for real, vvvvvv is probably going to win the vote and will be 50 cents and you could pair it with some one dollar game as well

Savant - Ascent