Out of sheer impatience, I want to have a central store of all the information we already have on the Knight Houses. If you're - like me - incredibly impatient to start painting but want to know more about the Houses first, this might be a diverting exercise.
If you have more info, post it below and I'll add it to the OP.
Imperial Houses
House Cadmus
• Character: Newly independent
House Degallio
House Griffith
• Colors: Bone with Blue and Red, Silver Trim
• Heraldry: Winged shield with a dragon on one side and half an aquila on the other.
House Hawkshroud
• Colors: Yellow and White w/Silver Trim
• Heraldry: Winged hawk coat of arms.
• Symbol: Hawk with its wing blocking its body.
• Character: Answers every call for assistance.
House Mortan
House Terryn
• Colors: Blue and Red w/Gold Trim
• Heraldry: Winged shield with a horse on one side and half an aquila on the other.
Mechanicus Houses
House Krast
• Symbol: Gauntled Hand crushing a Snake
• Character: Hates Chaos and the Chaos Titan Legions, brings Chaos heroes they capture back to their poisoned homeworld to die.
House Raven
• Colors: Red w/Hazard Chevrons
• Heraldry: Starburst behind a cog-shaped shield with the opus mechanicus on one side and their symbol on the other.
• Symbol: Triangular tower with the sun behind it.
• Character: The largest house
House Trainor
House Vulker
House Taranis
• Character: Fought alongside the loyal Mechanicus on Mars during the Horus Heresy.
Known Freeblades
Amaranthine
• Colors: Burgundy w/Gold Trim
• Symbol: The letter "X" and vine motifs
Auric Arachnus
• Character: Fought alongside the Ultramarines.
Crimson Reaper
The Firebrand
• Colors: Flame Motif w/Silver Trim
• Symbol: Burning Stick
• Character: Hot-headed and aggressive.
Klorian Saiche
• Colors: Burgundy w/Gold Trim
• Character: Stranded after the end of a war, negotiated with the Mechanicus to return home.
Gerantius
• Colors: Green w/Gold Trim
• Symbol: Barred gate/helmet thing.
Madrigal
• Colors: Purple w/Gold Trim
• Symbol: Skeletal Aquila
• Character: Protects his dead homeworld after failing to protect it from chaos.
The Obsidian Knight
• Colors: Black w/Silver Trim
Retribution Incarnate
• Colors: White and Red w/Silver Trim
• Character: Seeking revenge for his brother's death.
The White Warden
• Colors: White w/Gold Trim and some Yellow
• Symbol: Black sword on a white and yellow background.