If nothing else, you can be sure that if you pay attention and wait long enough, the game you so look forward to will be on sale eventually.
I have yet to buy a game on Steam without a significant discount.
I've had to wait quite a bit for some of them, but the vast majority will come on sale after a while.
gaming.stackexchange.com/users/1393/Aeo
It's common for them to discount GAME X in the run up/at the release of GAME X2.
So, for example, expect the Fallout 3 pack to get a price drop pretty soon because New Vegas is due in October.
gaming.stackexchange.com/users/3404/Drew
Short answer: no.
Slightly longer answer: price cuts Noooooo, sales yes.ie the Summer sale (no way to tell what tho) or discounts on iD games during QuakeCon
gaming.stackexchange.com/users/206/Tyronomo
Because the discounts and prices are negotiated with the publishers, you'd be better off trying to analyse on the publisher level rather than across Steam as a whole.
Additionally, because people would put off buying a game if they knew it was going to be discounted shortly, Steam will most likely purposefully avoid any such pattern (to ensure maximum revenue).
gaming.stackexchange.com/users/3383/Stu Pegg
The summer sale and winter holiday sales are predictable and always offer insane/awesome sales.
Your best bet would to check Steam every week and see is on on sale for that week.
For example I picked up Borderlands and its first three expansions for $22 one random week.
gaming.stackexchange.com/users/1770/Elpezmuerto
I haven't seen a pattern on new games but, I have seen that Valve will reduce the price of the previous version of their own games (and some that they distribute) just before a sequel comes out.
They also tend to offer discounts/packages on holiday weekends.
This is mostly on independent games and retro packages.
Finally, they tend to offer free games when celebrating an event like the release of Portal when the Mac version of Steam was released.
In the later case they like to drop hints that something is coming but like to keep the details a surprise.
gaming.stackexchange.com/users/1120/Chris Nava
In addition to what others are saying, I've noticed independent games are often given discounts relatively shortly after their release (like a month or two), while big-publisher titles maintain their price for a longer time.
gaming.stackexchange.com/users/122/Oak
When a similar or better game of the same genre is about to launch, it will become very likely that the older game will get a discount.
Modern Warfare 2 got a 33% discount in the week of the launch of Medal of Honor.
gaming.stackexchange.com/users/3375/Jader Dias
bad, old, and boring games will get discounts :)
Usually it happened on Thursday, so people could buy them on Friday to play at weekend.
Often presales are cheaper, because people don't know how bad is game, so they buy it to try.
Another time is when most players stop playing multiplayer game, so making 50-70% discounts bring more people(and money) as servers are already working and there is capacity for players.
And one more case: when new game is almost released (e.g. civ5), then previous versions get discount, because almost nobody will buy them after release.
gaming.stackexchange.com/users/3686/kusoksna
From observation, can I expect that a game will get a permanent price cut (or a weekend special deal) X weeks after its launch, or after the sales dropped by Y percent or whatever other reason?
Are Steam price cuts predictable?
gaming.stackexchange.com
<steam>
gaming.stackexchange.com/questions/7919
gaming.stackexchange.com/users/3375/Jader Dias
No. Summer and winter sales are predictable times. They will often discount the first game just before its sequel comes out. Whereas price-cuts per se are probably not predictable, sales are. Furthermore, educated guesses can be made at the publisher level or around the release of successor games.
This user believes that they cannot be predicted. Whereas price cuts cannot be predicted, sales can be. Users suggest that these things happen at the publisher level. 