Let's kick this off with some current Steam deals:
It's only been 2 months since this one got released, and it was worth the launch price, I'd say. A brilliant action adventure platformer, I very much enjoyed 100%ing it. For 25 bucks, its a steal.
As a reboot, however, it is not quite like the old Tomb Raider titles - if you want those, look to these here:
They've been on sale at 75% off multiple times before, but at those prices you can't really complain. Anniversary is basically a straight-up remake of the first TR, and all do a fairly decent job at being TR titles.
I'd recommend picking one based on its setting (read the store pages!) and going with that one for now; if you enjoy the game, you'll have plenty of opportunities to buy the others on another sale.
Huge Star Wars Weekend (May the 4th be with you and all) on Steam, and there are a few gems to be appreciated here, while other games are to be avoided at all costs.
If you enjoy FPS games, like the old Battlefield 2, then Star Wars: Battlefront 2 ($3.39 / 3,05€) might be right up your alley.
Solid shooter, interesting class-based system, lots of fun in multiplayer (the online servers were still fairly strong last time I checked) and it comes with a fairly interesting singleplayer component.
There's a good reason why people are still demanding Battlefront 3, and BF2 is currently #5 topseller on Steam.
If you prefer tactical shooters, go with Republic Commando ($3.39 / 3,05€).
This one puts you into the role of an elite clone trooper, leading his squad through various missions. You give the orders, your squad obeys. It also comes with a multiplayer coop mode, so that's something to consider.
PC Gaming Wiki has some tips to get it run well on modern machines
Now if you're more into RPGs, we've got you covered with Knights of the Old Republic ($3.39 / 3,05€) and the sequel ($3.39 / 3,39€).
If you enjoyed Mass Effect (one, not three, derp) and Dragon Age Origins, you'll know what you are in for. BioWare was responsible for the first game, while Obsidian did the second. Personally, I prefer the second, and it has received some MAJOR modding love recently, so it is a better experience than ever before.
These two games are also one of the main reasons why people were so excited for The Old Republic, btw.
At those prices, pick them both up!
I could also make a case for the very dated Jedi Knight and Jedi Academy games, but I am not sure they run very well on modern machines. If you are sure you can stomach the signs of age, I'd say go for it, though.
Now, please avoid the god-awful The Clone Wars: Republic Heroes game! It might be one of the most recent ones, but it is not worth the money. Rather than buying this, buy one of the ones above for a friend, and be glad that you saved yourself the pain and made somebody else a gift.
Be wary of The Force Unleashed as well! It might not be the worst game, but it is short and often frustrating, and the controls seem atrocious. The sequel is even shorter and more monotonous.
If you are a die-hard Star Wars fan and have cash to burn, I won't stop you, but curiosity kills the cat, as they say.
Aside from Steam, there's an EA Weekend going on over at GOG
Yes, we all hate EA these days, sure, but I don't even care. Getting most of the Good Old Games starting from $2.39 is great. Dungeon Keeper, Sid Meier's Alpha Centauri, Sim City 2000, Populous, Ultima....
Go check GOG's sale, this is a throwback to better times you should be aware of.