Marrying the spinster is hilarious; she has quite a mouth, and fights with a kitchen cleaver (it involves solving a quest for ST Cuthbert). There's another girl you can marry to join your group (a druid), and a gay pirate as well (who's secret desire is to become a dentist LOL). There's a wandering bard, and a Hill Giant chief you can recruit. Even the master of the moathouse, Lareth the Beautiful, will join your party as an NPC under certain circumstances. You can rescure Prince Thrommel and he'll join. Those are the oddballs -- then there are the more "normal" NPCs that people will recognize from the module who can join the party (some only once certain quests are completed, others for a share of the loot) -- Elmo, Spugnoir, Zert, Turuko & his barbarian pal, Furnok of Ferd, Otis, various men-at-arms, even Burne and Rufus, guardians of Hommlet.
The NPCs don't interact with you quite as much as in BG2, but they do say/do their own things, and can be pretty fun.