-The Black Knight Titan in the Holy Grail quest is a reference to the Black Knight in Monty Python & The Holy Grail.
-Use a Herring on the entrance door to the Grand Tree, and it says 'It cannot be done.'
-Canifis is probably a reference to the drug cannabis.
-The Dancing Knights in the Falador Party Room are a reference to Monty Python & The Holy Grail.
-The quest name 'Cold War' is a reference to the Cold War which actually happened.
-In the quest Rat Catchers, you can use Weeds with a Pot and light it with a Tinderbox to make a 'Smouldering Pot'.
-If you speak to Bob the Cat with an Amulet of Catspeak with a Cat following you, it engages a dialogue similiar to that of Star Wars Episode V: The Empire Strikes Back.
-The examine info of Slim Louie and Fat Rocco from the quest Fairy Tale Pt II: Cure a Queen, are both quotes from the movie 'The Godfather'
-The minigame "Vinesweeper" is a reference to the game "Minesweeper"
-The Zombie Dance emote that a player can unlock in Leo The Gravedigger strongly resembles a part of a dance from Michael Jackson's music video for his, song "Thriller".
-If you use an axe on one of the dead trees you will be given the message "You don't need any wood. What are you planning on doing, making them a fresh coffin"
-Royal Trouble Quest: If the player asks the guard in Miscellania if he or she can go down the dungeon before he or she gets permission to go down there, the guard will say "You're the regent Well I didn't vote for you!" This is similar to a phrase used in Monty Python and the Holy Grail.
Thanks for reading! I may make a part 2.
Note: Inspired by Bramblefang's Pokemon Fun Facts. Whoa! Whaddya know There's a fun fact in a fun fact page! :o