Redcloak is The Dragon and right-hand man (right-hand goblin?) to Xykon. The prequel book Start of Darkness shows that Xykon was, at one point, the dragon to Redcloak before becoming more powerful and carrying out a rather nasty gambit which involved making Redcloak kill his brother and then ordering him to turn the corpse into a zombie. That didn't work out too well however, because in the end Xykon is still working towards Redcloak's goals, even if Xykon thinks he is in charge.
Therkla is Daimyo Kubota's Dragon.
Crystal serves this role for Bozzok in the Greysky City Thieves' Guild.
Tarquin pretends to be the dragon to the Empress of Blood (ironically a dragon herself), and has his friend Malack as his own dragon.
Goblins has had two major Dragons so far — one for each major plot arc. Saral Caine was ("was" being the operative word) Dragon for Dellyn Goblinslayer in the Brassmoon Arc. Grem (until his Heel-Face Turn) and Riss were Dragons to Duv in Well of Darkness Arc. Not that Duv really needs a Dragon. She's more than Badass enough on her own...
Sluggy Freelance has had several Dragons in its long run. Most of them (Killum, Aylee, Kusari) have worked for the Hereti Corporation's Omniscient Council of Vagueness. Other notables include Lord Grater (Dragon to Zorgon Gala in the Punyverse arc) and Nash Straw (Dragon to Dastard Dickly in the "Phoenix Rising" arc) and Lord Horribus (Dragon to the Demon King in the Dimension of Pain stories).
Karnak from Dominic Deegan seems to have acquired a Dragon himself, in the form of Siegfried. He doesn't seem to be particularly loyal to Karnak, though, as Karnak appears to have some kind of hold over him, and even then has to smack him around a bit to make him do his bidding.
Also, Helixa seemed to be The Dragon to the leaders of The Chosen, first serving Raf MaLiksh, then to Caylin Bren (though it might've been the other way around for the latter, considering Helixa was pretty much second-in-command to MaLiksh himself before his death). She could also be viewed as The Dragon to Celesto Morgan after he joined the organization as well.
The Feline Emperor from Blade of Toshubi has his advisor, Toh, who himself has his own dragon in Lamika.
Much like each season having its own Big Bad, half of the seasons have its own Dragon in Ansem Retort:
Cloudscratcher: Narkethoness to Borzax and Agathoth to Emperor Vox, almost literally considering they're serpents.
Heartcore has Slade, the second most powerful demon in the realm of Asgar and the right hand man of Royce Lashiec. He also counts as The Dreaded, due to being a complete nutjob who loves to torture his foes in combat, but he has also shown intention to wanting to kill his own allies out of boredom and curiosity.