You played Baldur's Gate II with mods or without mods? It becomes a new game with the same main story and setting with mods. Lots of new stuff to discover and new reasons to play.
Also, if you didn't already, play it as a Wild Mage =)
Other RPGs I can suggest; (i will put a * near them if there is a bit action involved)
KOTOR 1-2
Jade Empire (*)
The Witcher Enhanced Ed. (1/2 *)
Fallout 1-2 (1/2 *)
Mass Effect 1-2 (*)
Star Ocean Last Hope (console game)(*)
The Last Odyssey (xbox360)(*)
Final Fantasy XIII (*)
Alpha Protocol (play on Xbox360 if you can)(*)
Deus Ex 1-2 (*)(would be nice to replay since 3 is coming soon)
Dragon Age: Origins and Expansion (*)
Hellgate London (*)(a bit meh but still a different taste)
Oblivion (with mods) (*)
Morrowind (with mods)(*)
Baldur's Gate II (with mods) (1/2 *)
Guild Wars (its online but free2play)(*)
Gothic series (*)(3rd one is meh but 2 rules)
The Bard's Tale (*)
The Temple of Elemental Evil (1/2 *)
Lionheart (1/2 *)
Icewind Dale 1-2 (*)
Might & Magic 6-7-8 (*) (ignore 9)
You can also go for uber classics like
Lands of Lore 1-2-3
Eye of the Beholder 1-2-3
Bloodnet
League of Hoboken
Menzoberranzan
Albion
Dune (more like a strategy rpg)
Privateer 1-2 (space sim with some rpg ish dialogue / consequence attitude)
DreamWeb
B.A.T. 1-2
I will try to come up with more names, have to check my list.
EDIT: Mod lists;
Baldur's Gate II + Throne of Bhaal (always play both together, TOB adds a lot to BG2 as well)
- Ascension
- BoM Item Pack
- CoM Encounters
- Redemption
- Volcano Pack
- Tzshop
- Yasraena
- WeiDU
- Unfinished Business
- BG2 Extras
- LOTS of Portraits (I can give you portraits if you want, it really adds a lot to the atmosphere)
Oblivion Mods:
- 300 Arcane University
- 5 New Races for Rens Beautiful People
- Adonnays Elven Weaponry
- Aldut Bookstore -> This is Junk btw I just remembered
- Akaviri Samurai Shop
- ALE dbarmor
- ALE silkrobe
- CM Partners
- Colour Wheels Sexy Casual Wear
- CuteElf11
- Elsweyr Anequina
- Frostmourne
- Glenvar Castle
- Griffon Fortress
- Guards
- Heart of the Dead
- ImpeREAL City Unique Districts
- Load Screens by Malachi
- Midas Spells
- Myths and Legends
- Naughty Joana
- Severians Katanas
- Sex Darkness
- Shinobi Set
- Skycastle
- Snow Dragon Temple
- xul (This is the Unique Landscapes mod(s) and it is 20 ESM files or so with 3-4 GB or so size but it REALLY worths it)
- Ndibella
- Ren Beauty Pack
The Witcher
- Definetly get the Enhanced Edition. It can be downloaded from the game website if you don't have the retail version of Enh. Ed.
- You can also download 2-3 additional adventure modules
Fallout 2
- There is a "complete" Fallout 2 mod out there that fixes A LOT OF things of Fallout 2 and adding lots of "left out" stuff
KOTOR 2
- Team Gizka was trying to complete the game, restoring all the left-out parts. Someone else finished it. I cannot recall the name but I downloaded it, so I guess you can Google it and find quite easily
Deus Ex
- There are some beauty mods and new adventure mods for Deus Ex. Some doesn't even require Deus Ex (but Unreal 2 etc lol).
While not particularly an RPG game per-say, Evil Genius is incredibly amusing. You should give it a look-see. There's also some nice mods at this site Evil Planet.