So Nice I Bought It Twice

[Kushan]

Crusader Kings 2. Bought it at release on Gamersgate, then bought the CK2 Collection later that year on Steam with all the DLCs. This was before it required Steam.

[Daroc]

Baldur's Gate 1 & 2
Fallouts 1-3 plus NV a couple of times
Morrowind, & Oblivion
SOTSE
CM1 all 3 of them
WOW at least twice
Witcher 3 twice
Most of the repurchases was for way less then the orignal with the DLC's thrown in which is why the repurchase
I am glad for steam and other distributors for keeping track of my games for me and letting me download multiple times the same game.

[Greybriar]

Which PC games are so good, you've purchased it more than once?
....

Too many to list, but I'll jot down a few:
Panzer General II
Master of Magic
Disciples I and II
Master of Orion I and II
Strategic Command
Heroes of Might and Magic I, II, and III
Fantasy Wars
Port Royal I and II
Tropico I, II, III, and IV
The Patrician I, II, and III
Dungeon Keeper
Age of Wonders I, II, and Shadow Magic
Conquest of the New World
Darklands
Castles I and II
King of Dragon Pass
Wasteland
Jagged Alliance series
Ultima series
Imperialism I and II
Settlers II
Neverwinter Nights I and II
Wizardry VI, VII, and VIII
Wing Commander I, II, and Privateer
King's Quest I, II, III, IV, V, and VI
Pacific General
and on and on.

I repurchased many of my old favorites from Good Old Games so I wouldn't have to put the disk in the drive in order to play them and sometimes to get a copy of a game without its original onerous DRM (I'm looking at you, StarForce!).

[DoctorQuest]

^That's my take. I don't rebuy a lot of games but when I can legitimately get away from mounting a CD to play a game I will do it.

[Martok]

Armada 2526 Gold
Descent
Descent 2
Lords of the Realm II
Medieval Total War Gold
Neverwinter Nights (Diamond Edition)
SimCity 4 (Deluxe Edition)
Shogun Total War Gold
Star Wars: Empire at War Gold
Star Wars: Knights of the Old Republic
Star Wars: Rogue Squadron

^That's my take. I don't rebuy a lot of games but when I can legitimately get away from mounting a CD to play a game I will do it.

That's mostly the case for me as well.  That, and/or my original copy of the game in question no longer wants to run on my computer, whereas digital-download versions (whether from GamersGate, GOG, Steam, or elsewhere) generally run on my machine just fine.