The central premise is that there is an apartment complex where fictional characters live where Eric (The Phantom of the Opera) and Jareth (The Goblin King) are roommates. Directly downstairs is the apartment where the objects of their obsession, Christine Daae and Sarah live. Regularly appearing neighbors are Commodore Noringtom, Inspector Javert, Aziraphale, and Crowley.
It began with a one shot cartoon by AsheRhyder
V-Day by *AsheRhyder on deviantART
Which inspired Roommates which begins here:
Roommates by *AsheRhyder on deviantART
It starts a little slow but once it gets going it's hilarious
Roommates 48 - Wizard by *AsheRhyder on deviantART
Roommates then inspired Pika-la-Cynique to do a fan-comic of a fan-comic and do the parallel series The Girls Next Door staring Christine and Sarah
GirlsNextDoor - Introductions by *Pika-la-Cynique on deviantART
Which gets even crazier than the original strip.
GirlsNextDoor09 - Dog's life by *Pika-la-Cynique on deviantART
Yes, that IS Jacob from Twilight. Poor bastard.
Both strips have multipart story arcs and they each refer to things that happen in the other. So far I've been able to keep up pretty well by switching back and forth reading 5 - 10 strips of each.