Roguey https://web.archive.org/web/20050205222300/http://www.bioware.com:80/bioware_info/about/ Neverwinter Nights
and its expansions have sold more than 2.6 million copies worldwide so far (2005) (three expansions and three editions)
Baldur's gate, released in 1998 has sold over 2 million units for PC and has won many industry awards; in 1999, BioWare released Baldur's Gate: Tales of the Sword Coast, a
Baldur's Gate expansion pack. It debuted at #1 worldwide and sold over 600,000 units
Baldur's Gate II: Shadows of Amn, was released in Sept. 2000 and continued the award winning story line of the Baldur's Gate series, selling nearly 1.5 million units so far; in June 2001 Baldur's Gate II: Throne of Bhaal was released, the expansion pack to the award winning Baldur's Gate II: Shadows of Amn, and the conclusion to the Baldur's Gate series, selling more than 500,000 units
Star Wars: Knights of the Old Republic- more than two million
http://www.ign.com/articles/2010/02/09/left-4-dead-2-dragon-age-sales-hit-3-million-each Dragon age origins has shipped 3.2 million copies worldwide since its launch in November 2009. I have no DLC numbers
Every post 2005 sales mention I've ever seen puts BG, BG2, and NWN all at "over/around two million" (Bioware must hate saying 2.1 million) however any of these legacy sales would be one of their gold/diamond/platinum editions which includes NVW DLC making it impossible to give base game sales. With the numbers difference Bioware is probably placing NWN at 2 million for launch and legacy sales with each expansion at 200k launch sales, which means the DLC significantly underperformed.
https://web.archive.org/web/2008100...s.latimes.com/2007/oct/12/business/fi-games12 Here's an example with NWN at 2.2 million and BG at 2.1 million despite being 2.6 million in 2005 if they are including DLC in these numbers. Obviously NWN was a middling product and they stuff all their sales reports of it with DLC while depriving other games the same benefit
TL;DR: dragon age origins was Bioware's most financially successful 90-00 game, NWN the fifth most