List of references on the Internet

Homestar Runner
On homestarrunner.com, there is a toon called "Pumpkin Carve-nival". In it, The King of Town is dressed as Mario. When the toon is over, click on him to unlock a secret minigame: "Super Kingio Bros."

Also, in the toon "Halloween Potion-ma-jig" The Cheat is dressed as Toad.

In the toon "Teen Girl Squad Issue 10" the character Tompkins is apparently playing a Mario game on an old Game Boy. Tompkins says he "has Bowser on the ropes" and a Koopa shell "pØwn"s So and So. Later on, the Ugly One says "Lets get it on like Diddy Kong".

The game "Stinkoman 20X6" features its very own version of the Minus World, Level -0, "NEGATORY". Unlike the Minus World, it is beatable (as well as part of the game), but is far glitchier than Minus World.

In Strong Bad E-Mail 153, Strong Bad is shown playing a videogame called "Sundae Driver". When he catches a cherry, a message that says "Cherry Get!" appears. This is a reference to "Shine Get!" from Super Mario Sunshine.

In Halloween Fan Costumes '06, one person dressed up as Homestar (who had his head visible from the costume) was next to a person in a Mario costume and Strong Bad said "Wait a minute, Homestar, who's that in your mouth? Did you eat Luigi?" He responded in "Yes Strong Bad, I ate Luigi. He tasted like mushrooms."

Kingdom of Loathing
KingdomOfLoathing.com is a text based RPG-type game, where you create a character out of the wacky classes they have available, then level up in a world where anything goes. In the Kingdom of Loathing there is a zone called the "8-Bit Realm," where there are various enemies from the NES-era for you to kill, including Bob-ombs, Koopa Troopas, and Goombas.

There are also various items you can buy throughout the Kingdom of Loathing that are Mario-esque in name, description, and use.

ScrewAttack.com
One of Screwattack.com's series, GameJew, features a guy dressed like Mario.