I want to play a D20 style RPG game that I haven't yet played, but I've already played:
Baldur's Gate 1 & 2
Icewind Dale 1 & 2
Neverwinter Nights 1 & 2
SW: KotOR 1 & 2 (Are you seeing a pattern here?)
AND I've played a bunch of somewhat-close-to-what-I-want-but-not-quite games like:
Jedi Knight series
Fallout NV (I keep meaning to get 3 though. I liked that one)
Mount and Blade
Morrowind and other assorted TES games
So I'm sort of stumped. Any recommendations?
Not sure how close to D20 they have to be (or necessarily are), but:
Fallout 1 and/or 2 and Planescape: Torment combined with the ones you've listed as played basically cover the classic/golden age examples of the genre.
Beyond that there's also the Divinity series, the recent Shadowrun game (a little underwhelming, but still worth a look), the Dragon Age series, maybe Spiderweb's games (Avernum et al), and I've seen a few recommendations for Temple of Elemental Evil.
In the not too distant future there's Divinity: Original Sin and Project Pillars of Eternity due in the first half of 2014.
Yah, "Divine Divinity" doesn't have a turn based system like Baldur's Gate or Fallout, rather it's more like Diablo in that regard. However the world has a lot of hidden items, quests and areas to go through and the questing is more like Baldur's Gate.
I think "Temple of Elemental Evil" is considered a good game because it's very focused. It takes place around a single village and such but because of that there's a lot of detail in character interaction and possible outcomes.
The Might and Magic series is also a good bet for RPG stuff. It's focused on combat with plot being more the reason to go out and kill things. 4, 4.5 and 5 I believe are considered the best of the series.
The Geneforge series is supposed to be good, but the graphics were a little too simple to keep my interest for long.
Edit: Oh, of course. The Ultima series are worth looking into as well. Ultima 6 and 7 specifically. Ultima 7 is a great RPG in the "roam the world" type. The earlier ones are a tad too old and the series started going downhill quite spectacularly after Ultima 7.