Pretty much every Tomb Raider.

FF7/8 and AOE2 were always on PC, but they also started to release former console exclusives on Steam like N2O.

If you simply mean 5th/6th gen era multiplatform games that initially had a PC release and have a Steam release today: well, there are tons of them.

Hmmm Resident Evil 1, 2 and 3. They were multi-platorm.

The Oddworld games ( Stranger's Wrath, Munch's Oddysee...), Legend of Kay, Megaman games, Metal Slug games, Grandia 2, Trails in the Sky, Valkyria Chronicles, Final Fantasy 3,4,5,6, Duck Tales, Ys Chronicles, Nights into Dreams, Jet Set Radio, Soul Reaver 1 & 2, Crazy Taxi, many Sonic Games...

Resident Evil 4 was added to the Humble Capcom bundle today

some other games that come to my mind:

Beyond Good & Evil
Devil May Cry 3 (but the port is pure shit)
Deus Ex
GTA III, VC and SA
Half-Life 2 (was on the original Xbox)
Max Payne 1+2
MDK 1+2
Prince of Persia: The Sands of Time
Quake III Arena (or simply get Quake Live for free)
Splinter Cell: Chaos Theory
Star Wars: Jedi Knight 2
Star Wars: Knights of the Old Republic
Unreal Tournament
Worms Armageddon

And some games are free nowadays (outside of Steam) like Command & Conquer 1-3, GTA 1+2 or Warzone 2100 (one of my favourite PS1 games).

Not that many PS1 games because multiplats weren't as common as today. And publishers are probably hesitant to re-release their old PS1 -> PC ports because most of them were garbage.

Many games on steam are garbage because everyone can upload their "games" with ease, what has that to do with that?

You think that the big publishers don't care about the reputation at all? Yeah, maybe I'm giving them too much credit.

Grandia 2 recently got a slight remaster on Steam. I know it was originally a Dreamcast game, and has already had a PC release, but I understand this newer release is a much better port.

Publisher Guy 1: "Hey we could make more money if we would rerelease our games on steam, why don't we do that?"

Publisher Guy 2: "No just no"

Publisher Guy 1: "Why?"

Publisher Guy 2: "Our games are garbage they don't deserve to be put on steam so we can make more money we are publisher who don't make games to earn money, we want to create games that make people happy, that inspires them, we want to make games with our HEARTS!"

Publisher Guy 1: "Ah ok wait WHAT!"

yes, you really give them too much credit in the end of the day they want cash just ask EA one of the biggest publisher.

...but old games from EA aren't bad ports because PC was always the lead platform for their older games. And they make old games compatible with modern operating systems. EA being shitty started mostly in the 7th generation.