Professor Flitwick
first name: according to the Harry Potter trading card game, it's Filius. Warwick Davis, in an interview with Comingsoon.com, indicated that JKR had told him that Flitwick's first name was Filius. That's still second hand, but it's pretty convincing.
hair: white ("a shock of white hair" PA5)
distinguishing features: very short ("tiny little Professor Flitwick")
voice: somewhat squeaky
age: "older," since he was a Dueling Champion when he was "younger," was teaching at Hogwarts during the 1970s. He is descibed as "ancient" (PA
House: head of Ravenclaw (BN)
field: Charms
office: seventh floor, near the base of the West Tower
interests: decorates with live fairies quite a bit
drink: cherry syrup and soda with ice and an umbrella

References:

• Professor Flitwick, the Charms teacher, was a tiny little wizard who had to stand on a pile of books to see over his desk. At the start of their first class he took the roll call, and when he reached Harry's name he gave an excited squeak and toppled out of sight. (SS7)
• Before Ron could answer, Professor Flitwick appeared at Malfoy's elbow.

"Not arguing, I hope, boys?" he squeaked.
"Potter's been sent a broomstick, Professor," said Malfoy quickly.
"Yes, yes, that's right," said Professor Flitwick, beaming at Harry. "Professor McGonagall told me all about the special circumstances, Potter. And what model is it?"
"A Nimbus Two Thousand, sir," said Harry, fighting not to laugh at the look of horror on Malfoy's face. "And it's really thanks to Malfoy here that I've got it," he added. (SS
• So the three of them followed Hagrid and his tree off to the Great Hall, where Professor McGonagall and Professor Flitwick were busy with the Christmas decorations....Professor Flitwick...had golden bubbles blossoming out of his wand and was trailing them over the branches of the new tree. (SS
• They had practical exams as well. Professor Flitwick called them one by one into his class to see if they could make a pineapple tapdance across a desk. (SS
• Hedwig was still angry with Harry about the disasterous car journey and Ron's wand was still malfunctioning, surpassing itself on Friday morning by shooting out of Ron's hand in Charms and hitting tiny old Professor Flitwick squarely between the eyes, creating a large, throbbing green boil where it had struck. So with one thing and another, Harry was quite glad to reach the weekend. (CS
• "And the fun doesn't stop here! I'm sure my colleagues will want to enter into the spirit of the occasion! Why not ask Professor Snape to show you how to whip up a Love Potion! And while you're at it, Professor Flitwick knows more about Entrancing Enchantments than any wizard I've ever met, the sly old dog!" Professor Flitwick buried his face in his hands.  (CS
• "It has happened," she told the silent staff room. "A student has been taken by the monster. Right into the Chamber itself."

Professor Flitwick let out a squeal. Professor Sprout clapped her hands over her mouth. Snape gripped the back of a chair very hard and said, "How can you be sure?"
"The Heir of Slytherin," said Professor McGonagall, who was very white, "left another message. Right underneath the first one. `Her skeleton will lie in the Chamber forever. "'
Professor Flitwick burst into tears. (CS
• Inside the castle, there was a buzz of Christmas in the air. Professor Flitwick, the Charms teacher, had already decorated his classroom with shimmering lights that turned out to be real, fluttering fairies. (PA
• Some of the teachers, like little Professor Flitwick, gave up trying to teach them much when their minds were so clearly elsewhere; he allowed them to play games in his lesson on Wednesday, and spent most of it talking to Harry about the perfect Summoning Charm Harry had used during the first task of the Triwizard Tournament.  (GF
• They were supposed to be practicing the opposite of the Summoning Charm today - the Banishing Charm. Owing to the potential for nasty accidents when objects kept flying across the room, Professor Flitwick had given each student a stack of cushions on which to practice, the theory being that these wouldn't hurt anyone if they went off target. It was a good theory, but it wasn't working very well. Neville's aim was so poor that he kept accidentally sending much heavier things flying across the room - Professor Flitwick, for instance. (GF