I talk to myself (not aloud, just in my mind) all the time while playing, usually commenting on NPCs or when I discover something good or impressive. Usually I manage to stay in character, too

Same here though its more like what the character would think to himself and not actually say. Some things i'll say are-
Why you little brat!- when listening to a little kid acting tough and mouthing off.
POWER- when a killing animation happens.
sixy nord momma- when seeing a sixy tavern maid.
Thieves..- Whenever i see a Khajiit.
Princess Stomper!- whenever i see a little bunny rabbit run past me on the road.
Better not get too close to those nice guys- when seeing a giant and a wooly mammoth in the distance.
I hope i dont bump into a giant camp- when traveling in the dark night across a vast field.
Burn and purge!- when casting a fire spell upon an enemy.
Ye gads! Am gonna die!- when being scorched by the blasting fire breath of a Dragon.
Ooo that oughta make the gut hurt real good- when finding a steel blade.
Sticky to the brain- when finding a orc mace.
I am not your father Luke- when dual casting a shock spell.
Ghostly..- when gazing upon the snowy winds sweeping across the freezing landscape of Skyrim.
Warmth- when entering a tavern and seeing a blazing fireplace.
Soft and comfy- when seeing a comfortable bed after just renting a room or entering my bedroom in my home.
Gut buster delight- when gazing down from a very very high cliff and thinking what would happen if i fell.
This better not give me a headache!- when drinking nord mead or ale.
Am i about to eat human flesh? Is this what my good guy character really wants?- After picking up some meat in a shack which had human bones under the table.