There is a top-ten thread floating around already, but someone mentioned they'd like to see top-tens from categories (Top 10 quest mods, realism mods, etc). I liked the idea, so I've decided create such a thread. So here are my top 10 lists, though some don't have 10 items to add...

TOP GAMEPLAY CHANGES/ADDITIONS
http://oblivion.nexusmods.com/mods/31668
http://oblivion.nexusmods.com/mods/5478 (considering trying http://oblivion.nexusmods.com/mods/41283 though, suggestions/comments welcome )
http://oblivion.nexusmods.com/mods/12466
http://oblivion.nexusmods.com/mods/41005
http://oblivion.nexusmods.com/mods/2037
http://oblivion.nexusmods.com/mods/14065
http://oblivion.nexusmods.com/mods/42640/ (awesome idea!)
http://oblivion.nexusmods.com/mods/35560
http://oblivion.nexusmods.com/mods/32914
http://oblivion.nexusmods.com/mods/19847


TOP QUESTS
http://oblivion.nexusmods.com/mods/17448
http://oblivion.nexusmods.com/mods/41012
http://oblivion.nexusmods.com/mods/39591
http://oblivion.nexusmods.com/mods/21989
http://oblivion.nexusmods.com/mods/11598
http://oblivion.nexusmods.com/mods/27029
http://www.lostspires.com/pages/downloads.htm
http://tesalliance.org/forums/index.php?/files/file/951-reclaiming-sancre-tor/
http://tesalliance.org/forums/index.php?/files/file/1288-knights-of-the-nine-revelation/


TOP NEW LANDS (same Tamriel worldspace or otherwise)
http://www.darkcreations.org/forums/topic/1927-relz-elsweyr-the-deserts-of-anequina/
http://obge.paradice-insight.us/wiki/LLOD_(Module)(link has a list of the TWMP mods towards the bottom)
...that's all I've used
Possibly http://silgradmodding.org/forum/index.php?page=Thread&postID=192384#post192384 (adding to next playthrough)


TOP REALISM
http://oblivion.nexusmods.com/mods/37088
http://oblivion.nexusmods.com/mods/24872
http://oblivion.nexusmods.com/mods/5197 (does this count?)
http://tesalliance.org/forums/index.php?/files/file/531-duke-patricks-follow-that-actor-rev-12/ (no more run+stop+run when following people)
http://oblivion.nexusmods.com/mods/22653
(Real-time Interactions) http://oblivion.nexusmods.com/mods/41526
http://oblivion.nexusmods.com/mods/21721
http://oblivion.nexusmods.com/mods/36313
http://oblivion.nexusmods.com/mods/18305
http://oblivion.nexusmods.com/mods/11478/http://oblivion.nexusmods.com/mods/11169 (makes a differnece with above's darker nights)


TOP COMPANIONS
http://oblivion.nexusmods.com/mods/28977
http://oblivion.nexusmods.com/mods/3027
(looking for a new (preferably beast) companion that works well with Vilja)


TOP hardcoe (harder game difficulty)
http://oblivion.nexusmods.com/mods/22193
http://oblivion.nexusmods.com/mods/21881
http://tesalliance.org/forums/index.php?/files/file/914-duke-patricks-melee-combat-no-recoil/
http://tesalliance.org/forums/index.php?/files/file/514-duke-patricks-combat-archery/
http://oblivion.nexusmods.com/mods/18065
http://oblivion.nexusmods.com/mods/16150
http://oblivion.nexusmods.com/mods/37385
http://oblivion.nexusmods.com/mods/31882
http://tesalliance.org/forums/index.php?/files/file/1294-fcom-convergence/!
http://oblivion.nexusmods.com/mods/35265

TOP CITIES (new or improved cities)
http://oblivion.nexusmods.com/mods/16513
http://oblivion.nexusmods.com/mods/33003
http://www.gamesas.com/topic/1250267-relz-arthmoors-villages-of-cyrodiil-thread-2/page__st__150__p__21430677__hl__arthmoor's%20villages__fromsearch__1#entry21430677
http://oblivion.nexusmods.com/mods/22828
http://oblivion.nexusmods.com/mods/38270
http://oblivion.nexusmods.com/mods/35434
http://oblivion.nexusmods.com/mods/22751
http://tesalliance.org/forums/index.php?/files/file/1180-kvatch-rebuilt/
http://oblivion.nexusmods.com/mods/33131
http://oblivion.nexusmods.com/mods/35908

TOP 10 Graphic Improvements
http://oblivion.nexusmods.com/mods/38350
http://oblivion.nexusmods.com/mods/10419(I overwrite parts of RTNM here, since I like the subtler feel of this one)
Robert's Males (no links, forum rules)
TGND (no links, forum rules)
Ozmo's Body Textures (no links, forum rules)
http://oblivion.nexusmods.com/mods/10763
http://oblivion.nexusmods.com/mods/35969
http://tesalliance.org/forums/index.php?/files/file/797-insanitys-improved-armoury-compilation/
http://oblivion.nexusmods.com/users/610829 (linked his profile)
http://oblivion.nexusmods.com/mods/41118

Perhaps my categories aren't the best, so feel free to use different ones if you'd like. I just thought I'd get the ball rolling.