So I was browsing the forums, checking what's new, what's up and I bumped into a post by Porscha in another topic that said: "I was going to make a thread the other day requesting someone to gather all the bigger mod projects listed into one thread so everything is easily trackable."
And I thought, I may just as well start a topic like that. If you know of any more big mods/are a creator of one, post in the topic and I'll add it to the first post. Feel free to post about major updates in your big mods as well and give me a brief description of your big mod (few sentences) and I'll put it here.
Alright, let's see if this catches on
Alphabetically:NEW LANDS AND COVERSIONS:
(I think they all include quests and some include many more things)
Algaesia
http://alagaesia-skyrim.fantasyboard.net/
(total conversion) Brings the world known form Eragon into Skyrim.
Andoran: Prologue
http://andoran.com/en/
Lands, battles, houses, and various other goodies.
Babylon
http://www.gamesas.com/topic/1379850-wip-babylon/
(lands, tweaks, story) The Project Babylon takes you into a complete new world. Babylon is going to be a German-speaking Total Conversion (there also shall be an English version), with a new area, new weapons, armour, buildings and plots, which won’t take place in Skyrim.
Enderal: The Shards of Order
http://enderal.de/?lang=en#contentInfo
(total conversion) The story of Enderal is not set in the Elder Scrolls world of Tamriel, but takes place in its own universe, creating a new, interesting world completely unrelated to Skyrim.
Ethas: Embrace of Destiny
http://www.moddb.com/mods/ethas-embrace-of-destiny
In Embrace of Destiny, you will explore the lands of Arelia and Virardan, two countries currently at war with each other. Your role starts you out as one of the five famous Captains of the Arelian Army. Choices will be made, and sides will be chosen. The only question that remains, is, will you become the hero, or the villain?
Falskaar
http://www.youtube.com/watch?v=BxWpfz06sgw&feature=youtu.be
(lands, story) Introduces new land of Falskaar.
Isgaard
http://prometheusmod.proboards.com/index.cgi
(lands, models, story) Introduces new land of Isgaard.
Kamdoon
http://www.gamesas.com/topic/1385553-clints-full-open-world-mod-unnamed-as-yet/
A massive area in High Rock, Above Daggerfall In the Wrothgarian Mountains between Vermeir and Thorvale.
MERP
http://merp.straygenius.com/forum/index.php
(lands, races, quests, creatures, meshes) Middle Earth Roleplaying Project aims to recreate Tolkien's world in the Skyrim engine.
Moonpath to Elsewyr
http://skyrim.nexusmods.com/mods/9782
(areas, quests, creatures, meshes) Its a Mod attempting to give an Elsweyr experience to any player of Skyrim regardless of race.
Silgrad Tower
http://silgradmodding.org/
(lands, quests) Silgrad Tower is a mod for The Elder Scrolls V: Skyrim that will initially encompass the area around the city of Silgrad Tower in western Morrowind (http://silgradmodding.org/?p=251). Upon completion of this portion, we will expand north, creating the cities of Soluthis and Blacklight.
Tytanis
http://skyrim.nexusmods.com/mods/1601
(uh, everything and their cat)Huge multi-component modification, still under development. To contain quests, land, NPCs in the upcoming future.
BIG QUEST MODS:
Dragonborn Legacy
http://forums.nexusmods.com/index.php?/topic/467279-the-dragonborn-legacy/
A big quest mod including various tweaks regarding the Dragonborn.
Kind of Blue
http://www.gamesas.com/topic/1330846-wipreq-kind-of-blue/
A big quest mod.
Lamplight
http://www.gamesas.com/topic/1392289-beta3-lamplight-the-bandit-guild/
The premise of the mod is to create a new guild of Bandit outlaws.
sixy Maids of Skyrim
http://skyrim.nexusmods.com/mods/16021
Multi-act quest mod.
BIG COMPANION MODS:
Aela the Huntress
http://skyrim.nexusmods.com/mods/11450
A huge expansion to Aela the Huntress from Vanilla Skyrim. Thousand lines of dialogue, romance and marriage options in the work.
Atvir Dres
http://skyrim.nexusmods.com/mods/19348
Fully voiced male companion Atvir Dres with expansive relationship possibilities.
Gabby
http://skyrim.nexusmods.com/mods/9070
Fully voiced companion with her own personal quest and marriage options.



I hope some modders might find this topic to their liking and post an update from time to time. Keeping it visible could do some good to every mod mentioned here, as long as people will be interested in tha easy browse 