My wishlist tells me that these are the games that I'm waiting for:
Blackguards
The Banner Saga
Heretic Kingdoms: The Inquisition
Wing Commander: Armada
Democracy 3
Battle Worlds: Kronos
Entomorph: Plague of the Darkfall
Aarklash: Legacy
Privateer 2
The Raven
Pandemonium 2
Rayman Origins
Strategic Command: European Theatre
Ehterlords

Which seems about right.

I have many games on my wishlist but lets see.. The Rayman series(Forever, 2, 3) would be nice to have on sale, also the Oddworld games are just waiting to get on my shelf. Desperados: Wanted Dead or Alive wouldn't hurt either.

After the latest sale... almost nothing, it seems. The only game on my wishlist is Theme Park.

I'm sure there are a few games I'd buy if they went on sale though, like Rogue Legacy.

Minecraft.
It will probably be on sale in about 10 years.

heretic kingdoms but I guess is not going to be on sale in the near future

Go on sale:

Battle Worlds: Kronos
Aarklash: Legacy
Shadowrun Returns

For sale here at GOG:

Blackguards
The Banner Saga


I'm really curious about the recently renamed Incognita→Invisible, Inc. too, but since it's in alpha, it'll be a while.

That question is equivalent to ask for the top entries in the wishlist.

Well, they are Eador.Genesis, Psychonauts and a game called The Inner World but I don't remember what it should be.

As discount I expect more than 50%. I have enough other games to be able to wait until I can obtain 60% or more. If they come with other games bundled than at least 75%.

Given my behemotic backlog and the fact that I already own all the games that I truly truly urgently wanted, I don't want to pay more than $10 for the few remaining games I have a vague interest for. And they are all around$20 or more.

So, i'm just (very) patiently waiting for some of the big 'expensive' gog games to drop for a sale. Heck, one was even half priced during christmas, but it wasn't sufficient for me. Still too expensive compared to the actual level of interest I have in being currently able to play it...

EDIT: Ah, outside of gog there are a few. Sometimes it's mixed with waiting for them to go DRM free, more than on sale, but sometimes it's hopeless, and, while i'm quite interested in playing them, I consider that the DRM is a cost in itself, I don't want to pay too much for a merely rented game, etc. And unfortunately, I don't check these sites frequently enough to get the sales opportunities. So, in practice, it just comes down to giving up on these games, or checking, every 2 years, if obsolescence has dropped the price...

That's not the point... What Rohrer (the Castle Doctrine dev) says is that nowadays most people wait for a sale although they would pay the asked release price. We've reached a point where it is stupid to buy a game at release at full price (except you want to "support the devs" or something like that), because everyone knows that there will be a huge discount in the next few weeks or months. People don't like to spend $60 for a game when they know that they can get it for $20 three months later.

The discounts are too huge and they're coming too fast. According to Rohrer, that's why games are selling worse in the first weeks after release. And this is hurting devs/publihers and players. They "have to" wait for a sale, there are fewer people in multiplayer and people who bought the game at release feel ripped off when they see the huge discounts. Tomb Raider 2013 is a prime example. It was 75% off after four months. You paid the full price for it? <steamspeak>*lol* omg, y u so stewpid? u should of known to w8 4 salez!</steamspeak>

What, on GOG? Nothing really. About 90% of my wishlist is stuff I already own on disc, and the rest I'm in no hurry to play.

Outside of that, I'm waiting for Dishonored GotY for $5 or less. Might and Magic 10 will probably be the same story.

It's not that I'm not willing to pay more for those games. It's that I'm not willing to pay more for crippled games.

The sale I'm waiting the most isn't for a GOG game, but Steam.
Iron Front: Liberation 1944. Why ? Because I love ArmA series, and Iron Front is using the ArmA II's engine. And it's WW2 related, so different experience than ArmA.

Broken Sword 5

I'm waiting for sales on Aarklash Legacy, Blackguards, Age of Decadence, UnderRail, Banished, Legends of Eisenwald, ROA: Blade of Destiny, BG1&2 Enhanced, World of Zoo

There's probably a rather clear red line going through that list xD

Do you happen to have a source indicating these games arriving to GOG?