Mentioned in dialogue
Leonard, Sheldon and Wolowitz discuss it; later, Sheldon sings a number from it.
Sheldon says that he has a "Justice League" membership card.
Raj's parents want to hang up from their web-cast because it's time for Doogie Howser to air, and they dont want to miss it. Then Leonard, Sheldon, and Wolowitz discuss why Doogie Howser might be so popular in India.
After Wolowitz imitates Raj on the phone, Raj tells him that he made him sound like a Simpsons character.
Wolowitz bets that "Scrubs" is loved in India for the same reason "Doogie Howser" is.