Buckler in Friendly Inn Arm with the gnome inside the inn (give +1 to constitution, always good)
Robe of the (alignment) archmage with the wizard on High Wedge (only good or neutral in this store), also buy here a potion case, protection from magic scrolls (save them for later) and spells to fill your mages spellbooks.
Shadow Armor (for thiefs) with the Blacksmith in Beregost, also he has a poison dagger that is nice.
In Ulgoth's Beard, get the +3 staff, the Cloak of displacement, the harp (for bards if you have one) and the wand of paralization (this one is awesome to have)
In Baldur's Gate get all the arrows of detonation and of dispel you can get in Sorcerous Sundreon store (BG entrance), they're expensive so you gonna spend something like 50-80k more or less to buy them all (based on your charisma+reputation), but they're worth it.
Yes. Thank you for pointing out number one! Starting a new game, soon~
In general I believe you'll have more than enough money to spend it on anything your heart desires (or nearly anything) in Baldur's Gate 1. In the second one, it might be a bit tougher with all the choices, but you can still get lots.
The given suggestions are all great, but I'll add one more for sporty reasons :
At High Hedge, Thalantyr sells the Claw of Kazgaroth. While its bonuses might not be good for warrior classes, if you have a mage, cleric, thief or similar with a constitution of 18, you might want to invest in it. Keep in mind though - it's a cursed item and cannot be removed unless you cast a remove curse spell or you purchase one as a service off a temple.
At the smithy in Beregost, the merchant there sells some quite tasty items, amongst them are the Full Plate Mail (one of two in the entire game), the Dagger of Venom (I think that's the name, it's an improved version to the otherwise very free Dagger +2, it's a good item against spellcasters) and the crossbow of speed (if you prefer Crossbows to Bows, that's arguably the best crossbow in the game)
The Necklace of missiles from various places also comes in handy. Baldur's Gate 1 doesn't have a huge collection of amulets, some of which aren't that useful at all. But the necklace of missiles is really good for steady crowd control. Keep in mind though - it will hurt YOU too!
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The given suggestions are all great, but I'll add one more for sporty reasons :
At High Hedge, Thalantyr sells the Claw of Kazgaroth. While its bonuses might not be good for warrior classes, if you have a mage, cleric, thief or similar with a constitution of 18, you might want to invest in it. Keep in mind though - it's a cursed item and cannot be removed unless you cast a remove curse spell or you purchase one as a service off a temple.
At the smithy in Beregost, the merchant there sells some quite tasty items, amongst them are the Full Plate Mail (one of two in the entire game), the Dagger of Venom (I think that's the name, it's an improved version to the otherwise very free Dagger +2, it's a good item against spellcasters) and the crossbow of speed (if you prefer Crossbows to Bows, that's arguably the best crossbow in the game)
The Necklace of missiles from various places also comes in handy. Baldur's Gate 1 doesn't have a huge collection of amulets, some of which aren't that useful at all. But the necklace of missiles is really good for steady crowd control. Keep in mind though - it will hurt YOU too!