I've always been inspired by Norse Mythology. The tale of Thor's Visit to Jotunheim, in particular.Thor's Visit to Jotunheim
The benches and the passageway behind them were filled with giants, drinking, eating, shouting at the top of their voices. Before him a group of six, with iron-gray topknots and patchy beards like Skrymir's, were wrangling. One drew back his arm in anger. His elbow struck a mug of mead borne by a harassed-looking man who was evidently a thrall. The mead splashed onto another giant, who instantly snatched up a bowl of stew from the table and slammed it on the man's head.
Down went the man with a squeal. Skrymir calmly kicked him from the path of his guests. The six giants burst into bubbling laughter, rolling in their seats and clapping each other on the back, their argument forgotten.
"Hai, Skridbaldnir!" Skrymir was gripping another giant on the bench by the arm. "How's every little thing wit' you? Commere, I wantcha to meet a friend of mine. This here guy's Asa-Thor!"
Skridbaldnir turned. Shea noticed that he was slenderer than Skrymir, with ash-blond hair, the pink eyes of an albino, and a long, red, ulcerated nose.
"He's a frost giant," whispered Thjalfi, "and that gang over there are fire giants." He waved a trembling hand toward the other side of the table, where a group of individuals like taller and straighter gorillas were bowling at each other. They were shorter than the other giants, not much more than eight feet tall. They had prognathous jaws and coarse black hair where their bodies were exposed. They scratched ceaselessly.
Right in front, facing him, flanked by two guards who carried the curious burning swords, sat the biggest giant of all - a giant dwarf. That is, he was a full giant in size, at least eleven feet tall, but with the squat bandy legs, the short arms and huge neckless head of a dwarf.
- excerpted from "The Roaring Trumpet" (1940) by L. Sprague de Camp and Fletcher PrattThe Roaring Trumpet
Hill giants have tan to reddish brown skins, brown to black hair, and red-rimmed eyes. They typically dress in rough hides or skins.
Frost giants have dead white or ivory skin color, blue-white or yellow hair, and pale blue or yellow eyes. Their build is basically similar to a muscular human, with appropriate size differences.
Fire giants are very broad (about 6' at the shoulders), looking almost like dwarves. Their skins are coal black, hair is flaming red or bright orange, and eyes are deep red.
- Monster Manual (1977) by Gary Gygax