Online Board and Party Games

Board Games

Board Game Arena many different board and card games - needs free account
BuddyBoardGames Azul, Crazy Eights, Farkle, Oh Heck, Spades, Wizard, Uno, Yahtzee

Word Games

Scattegories aka Categories, Guggenheim
One Word co-operative (Just One)
Enigma / Decryptr 2 teams (Decrypto)
Taboo
Plantaingrams (Bananagrams)
Codewords 2 teams (Codenames)
Person Do Thing

Drawing Games

Skribbl
Draw Battle
Broken Picturephone (same game as Gartic Phone)
Gartic Phone (same game as Broken Picturephone)
  The random noun generator might be useful.

Social Deduction Games

One Night Ultimate Werewolf 3 - 29 players
Secret Sith 5 - 10 players
Avalon 5 - 10 players (The Resistance: Avalon)
Chameleon 3 - 12 players

Trivia Games

Wits & Wagers 2 - 7 players (New window without toolbars)

Other Games

Jackbox
Longwave 2 teams (Wavelength)
Joking Hazard (Adults only)