A character named "Lord Foreshadow" extols the general awesomeness of nights in Neverwinter. Neverwinter Nights was still in development at the time of BG1's release.
The game also has a character named Pallonia who mentions "a city where winter never rears its ugly head" that "will soon welcome the return of a multitude of citizens." Neverwinter Nights was also the name of an old MMORPG that shut down in 1997.
In the field just south of Beregost, you can run into a character named Bub Snikt who can smell ogres nearby and claims that what he does ain't pretty. 'Snikt Bub' is a nickname of Wolverine...
And of course, there's Wolverine's penchant for calling people 'bub', and 'snikt' being his claws' signature sound effect.
Repeatedly clicking on Safana results in the sultry-voiced thief quoting Mae West, telling you "When I'm good, I'm very very good. But when I'm bad...I'm better," and "Between two evils, I always choose the one I haven't tried."
Shar-Teel paraphrases a couple of quotes from Predator: "If it bleeds, I can kill it," and "I don't have time to bleed."
The paladin Ajantis will sometimes tell you "My honor is my life." This is, word for word, the creed of Sturm Brightblade from Dragonlance.
There's an NPC named Peter of the North (encountered during the wyvern hunt quest). Peter North is the screen name of a well-known adult film actor. In the game, Peter of the North calls himself a "master woodsman," just in case you thought it was a coincidence.
In the city of Baldur's Gate there is a man named McFeelie who, if spoken to, tells you about his speedy delivery.
When Quayle offers to join the party outside Baldur's Gate, he says, "Surely this leads us a familial bond of sorts...." The player can then turn him down with the response, "No, and don't call me Shirley."
The password to the Baldur's Gate Thieves' Guild? Fafhrd.
Baldur's Gate II
Garrick, an unrecruitable NPC in this game, is involved in a subplot that is very much like Cyrano de Bergerac.
When the party investigates a string of bizarre murders in a remote village called Imnesvale, one of the potential culprits is an old legend about the Umar witch, living in the hills. Apparently, a trio of apprentice mages vanished into the hills some years ago while looking for the witch, leaving behind one of their journals. Sound familiar? The journal, which you can get a copy of find multiple copies of, is called "The Umar Witch Project".
In Throne of Bhaal, the Spectator Beholder shows up again in Sendai's Enclave. He mocks Captain Egeissag by saying "Oh Captain, my captain!" (quoting Dead Poets Society). When asked why he's doing that (bearing in mind the Spectator is about as un-Beholder like as his race comes) he simply says he's always wanted to say that.
In Athkatla's commercial district is a huge store of magical items. If you go to the top of the store, you'll find some pictures of Hank and Bobby, two of the characters in the 1980's Dungeons & Dragons cartoon. Clicking on them reveals that apparently all of the teens (or at least Hank, Bobby and Uni) never made it back to their own world, as they were eaten by Tiamat.
A moose and squirrel have been conspicuously caged together at the circus in Waukeen's Promenade.
On the western side of Brynnlaw, there are two pirates having a disagreement of sorts which culminates in a fight to the death. After slaying his opponent, the victor humorously quips, "Fairly warned be thee, says I."