Some other notable sales that I can at least comment about:
XCOM: Enemy Unknown is a very solid turn-based, squad tactics game. YMMV on replayability, but your first go through is likely going to be very enjoyable, especially if you're a fan of tactical games.
Dishonored is a very, very neat game. Gameplay is this mix of stealth (with decently realistic stealth) and assassination with some magic powers thrown in. The gameplay is very solid, the story is enjoyable, but the biggest part of the game is the world they invent. After finishing Dishonored, the only thing I could think of was that I wanted to play Dishonored 2, if/when it comes out. I didn't want a sequel because they left the story hanging, or because there was a lot of potential to be realized, but because the world itself was so interesting that I wanted to be immersed in it again.
However, I'm pretty sure it has gone on sale for cheaper, + the DLC.
Earth 2150 Trilogy. This is a really old, 3D RTS that had some mechanics I haven't seen since, with a story that has stuck with me ever since I read it in the manual. There are three different groups that are decently unique (similar but not as extreme as StarCraft). All units are built by taking a chassis (you can research new ones) and slapping down weapons and armor on it and saving that design. Maps also have dynamic over- and under-worlds. You can raise/lower terrain on the surface and dig tunnels underground. If you've played Warzone 2100, Earth 2150 is very similar but the feel is quite different - resources are scarce and everywhere pretty much needs your attention, so you need to do everything you can to not make any mistakes. It's actually incredibly appropriate, given the story. This complete pack is about as cheap as I've seen it, but you might be able to find it on sale on GoG for a couple bucks less.
Age of Empires III: Complete. Here's a guide to enjoying Age of Empires III. Imagine it was named anything else so it didn't have to follow up on Age of Empires II. Done. Seriously, AoE3 is actually a pretty good game. It has interesting epoch mechanics, the different civilizations have pretty unique (and enjoyable) units and playstyles, and the game is laid out so as to hold your interest from the very beginning (which tends to be a bit slow in RTS) to the very end. Some people may not enjoy the mechanics as others would, but that's standard taste in games. AoE3 mostly got a bad rap because it has "Age of Empires" in the name and it was very different from previous iterations. I've not seen this for less, but I also haven't been looking.
Compare that to Empire Earth 2, which didn't change much at all except for adding a few bells and whistles while being inferior in pretty much every way to the original Empire Earth.
The Settlers 7.... bleeeeehhhhhh pass. Felt like a kids game to me, I honeslty wouldn't pick it up for free because it was just so bland of a game, but that could just be me.
Fallout: New Vegas. Goes on sale cheaper in other places (Like GameStop/Impulse).
Syberia + Syberia II. Interesting Myst-lite-like games. The second game has some really gorgeous set pieces and animations.
To the Moon. Oh my god buy this game. If you don't own it, buy it. I don't care what genres of games you like, just buy the damn game, because it's not so much a game as it is an experience. Buy it, set aside around 4 hours, and play through it in one sitting, because it's like a movie. You will thank me. Also, buy it.
MDK/MDK2. MDK is just so super old and it's so clunky and strange for a shooter and the mechanics don't make sense and etc. MDK2 was a super interesting game that I first played as a demo on the Dreamcast. I picked it up from GoG to play the full version, but I couldn't enjoy it because there were technical difficulties (game-breakingly long cutscenes, dialogue glitches, game crashes, etc.). There's an MDK2HD on sale, but I don't know if it fixes any of that. Do some research on it if you think you'd like a zany shooter.
Grand Theft Auto IV. Goes on sale for cheaper elsewhere.
For Tropico and Dust: An Elysian Tail blurbs, you can search this thread.
Tom Clancy's Rainbow Six Vegas 2. I got this game for free, but I'd say that it's worth 5 bucks. It's a decent tactical/arcade FPS.
Beyond Good and Evil. Classic. Worth more than $5, but hey, they'll give it to you for just that.
Railroad Tycoon Collection. When you talk about exceptional Tycoon games, you think of Transport Tycoon, Rollercoaster Tycoon and Railroad Tycoon II (though Railroad isn't related). A solid economics game, with realistic supply and demand, stocks, bank bonds, the works. YMMV on whether you prefer Railroad Tycoon II or Railroad Tycoon 3, but both are great games IMO.
Mafia II. Kind of like GTA if there were less things to do and GTA had a more substantial plot. Not sure that it's worth $20 though.
GalCiv II: Ultimate Edition. You can search the forums for debate on this. Basically, some people though it was a decent game, others really disliked it.
Prince of Persia (The Disney-like [or was it just Disney?] one). A lot of people didn't like a PoP game that wasn't as hardcore as stuff like Warrior Within. However, I did enjoy PoP. It's a much more casual/forgiving entry in the PoP series that focuses a lot on platforming and mobility. It's probably worth $5.
Depths of Peril. Neat Diablo II-like, but just get Paths of Exile instead for free.
Tribes: Ascend GOTY. This was a money-grab, plain and simple. Hi-Rez isn't updating the game. The player-base isn't that big. It's decent, but you'll probably only see ~200 people online at a time. You can play the game for free (and it is very fun), and if you like it, play enough that you unlock what you want with XP gained by playing.
X Superbox. Goes on sale for way cheaper.
World in Conflict: Soviet Assault. This is basically the gold version of the game. Very, very interesting RTT game. You'll likely get your money's worth.
Crysis Maximum Edition. Crysis came out in 2007. It maintains arguably better graphics than current-gen FPSes (*cough*CoD:Ghosts*cough*), was a solid shooter, had a could-have-been-revolutionary approach to how you played a given level, and had an interesting story. The only thing that hurt it was that you pretty much needed a 2008 PC in order to play it. Or a 2009 PC. Or a 2010 PC.
PopCap collection. Do not confuse with PopTop. Then remember PopTop. Then cry.
Red Faction Collection. Goes on sale for cheaper.
To the Moon. Yeah, I already did this, but I just wanted to reiterate the immeasurable need you should have to purchase this game.
Now to think about picking up the Portal bundle and the Sega Genesis collections.