The only confirmed volcanoes we have are the two in your question.
The Fourteen Flames
The Fourteen Flames around Valyria are what eventually erupted and caused the Doom.
To this day, no one knows what caused the Doom. Most say that it was a natural cataclysm—a catastrophic explosion caused by the eruption of all Fourteen Flames together.
The World of Ice and Fire, Ancient History: The Doom of Valyria
Dragonmont
The volcano on Dragonstone and is noted to still be active as steam rises from its vents.
And yet . . . and yet . . . the comet burned even by day now, while pale grey steam rose from the hot vents of Dragonmont behind the castle, and yestermorn a white raven had brought word from the Citadel itself, word long-expected but no less fearful for all that, word of summer's end. Omens, all. Too many to deny. What does it all mean? he wanted to cry.
A Clash of Kings, Prologue
However, there is mention to other volcanic activity such as the following.
Hot Springs
There are hot springs at Winterfell which are warmed by volcanic activity beneath the ground and the maesters have noted this. I've seen mention that the Dreadfort is also heated by hot springs but I can't track down a reference for this at the moment.
Hot springs such as the one beneath Winterfell have been shown to be heated by the furnaces of the world—the same fires that made the Fourteen Flames or the smoking mountain of Dragonstone. Yet the smallfolk of Winterfell and the winter town have been known to claim that the springs are heated by the breath of a dragon that sleeps beneath the castle. This is even more foolish than Mushroom's claims and need not be given any consideration.
The World of Ice and Fire, The North: Winterfell
Brimstone
There are various mentions to smelling brimstone and the rock brimstone, however, in Dorne there is a river called Brimstone. This is known for it's yellow waters which stink of sulfur.
The Brimstone is a far more placid stream, but its cloudy yellow waters stink of sulfur, and the plants that grow along its banks are strange and stunted things.
The World of Ice and Fire, Dorne
Mother of Mountains
Although not confirmed either way it has been speculated on that the Mother of Mountains is a dormant volcano with the Womb of the World also being a part of the volcanic activity that was once there.
The horselords have only one permanent settlement: the "city" they call Vaes Dothrak, which stands beneath the shadow of the lonely peak they call the Mother of Mountains, beside a bottomless lake they name the Womb of the World. It is here that the Dothraki believe their race was born. No true city, Vaes Dothrak has neither walls nor streets. Its grassy thoroughfares are lined with stolen gods, its palaces made of woven grass.
The World of Ice and Fire, Beyond the Free Cities: The Grasslands
Casterly Rock
Again although it's speculation I've seen it mentioned that the Rock is likely a volcanic plug and similar to Arthur's Seat in Edinburgh. I'm no geologist but from what I've read gold can also be found where there was once volcanic activity this supports the theory more.
Skagos
Although not confirmed again Skagos does have mountains.
Dareon knew the songs as well. When the bleak grey peaks of Skagos rose up from the sea, he joined Sam at Blackbird's prow, and said, "If the gods are good, we may catch a glimpse of a unicorn."
A Feast for Crows, Samwell II
It's also mentioned that the Skagosi trade obsidian blades and arrowheads so they are likely to have dragonglass deposits on their island.
For most of recorded history, they have remained an isolated, backward, savage folk, as like to murder those who land upon their isle as to trade with them. When they do consent to trade, the Skagosi offer pelts, obsidian blades and arrowheads, and "unicorn horns" for goods they desire.
The World of Ice and Fire, The North: The Stoneborn of Skagos
Hardhome
There is speculation that the disaster at Hardhome was the result of volcanic activity and looking at the description it is possible. Though of course it could have just been an ordinary fire.
He did. Hardhome had been halfway toward becoming a town, the only true town north of the Wall, until the night six hundred years ago when hell had swallowed it. Its people had been carried off into slavery or slaughtered for meat, depending on which version of the tale you believed, their homes and halls consumed in a conflagration that burned so hot that watchers on the Wall far to the south had thought the sun was rising in the north. Afterward ashes rained down on haunted forest and Shivering Sea alike for almost half a year. Traders reported finding only nightmarish devastation where Hardhome had stood, a landscape of charred trees and burned bones, waters choked with swollen corpses, blood-chilling shrieks echoing from the cave mouths that pocked the great cliff that loomed above the settlement.
A Dance with Dragons, Jon VIII
Hardhome was once the only settlement approaching a town in the lands beyond the Wall, sheltered on Storrold's Point and commanding a deepwater harbor. But six hundred years ago, it was burned and its people destroyed, though the Watch cannot say for a certainty what happened. Some say that cannibals from Skagos fell on them, others that slavers from across the narrow sea were at fault. The strangest stories, from a ship of the Watch sent to investigate, tell of hideous screams echoing down from the cliffs above Hardhome, where no living man or woman could be found.
The World of Ice and Fire, The Wall and Beyond: The Wildlings
