If anyone has a reasonably long, fun and interesting questline that is not a faction or the main quest let me know. Also post where to find them.

Already in the game?

The Forsworn Conspiracy in Markarth, it triggers as soon as you enter the city.

Yep Forsworn Conspiracy is a fun questline. Its kind of like a detective quest at first so have fun!

http://www.uesp.net/wiki/Skyrim:The_Affairs_of_Hagravens

Just did this one the other day. Not only is the dungeon amazing but the quest is kind of fun. Not too challenging as you can let the Hagraven do most of the work but still interesting.

Forsworn Conspiracy is good but be warned if you like keeping a large population in Markarth, because a lot of people will or can die.