TvTropes has a page TVTropesAsAGatewayDrug where individual editors (tropers) list things the wiki got them interested in. I've sorted the page by popularity, and these are the top ten:

• 1: OrderOfTheStick (30 people)
• 2: Discworld (26 people)
• 3: ThatGuyWithTheGlasses (24 people)
• 4: MyImmortal (22 people)
• 5: AvatarTheLastAirbender (22 people)
• 6: TengenToppaGurrenLagann (20 people)
• 7: Xkcd (18 people)
• 8: GunnerkriggCourt (18 people)
• 9: Firefly (18 people)
• 10: NeonGenesisEvangelion (16 people)

Of these, I already know I like order of the stick, discworld, xkcd, and firefly. So I guess I should have a look at the other six.