In the same vain as the Firefox extension list, I thought I would put together a list of the UI mods I currently am using in WoW. I generated this list by taking a snapshot of my /addons folder then removing the blizzard frames.
!BugGrabber
Ace2
ag_UnitFrames
Atlas
AtlasBattlegrounds
AtlasDungeonLocs
AtlasFlightPaths
AtlasLoot
AtlasOutdoorRaids
Auctioneer
aUF_Layouts
aUF_RangeCheck
BeanCounter
BtmScan
BugSack
Cartographer
Cartographer_Battlegrounds
Cartographer_Cleanup
Cartographer_Coordinates
Cartographer_ExtractGas
Cartographer_Fishing
Cartographer_Foglight
Cartographer_GroupColors
Cartographer_GuildPositions
Cartographer_Herbalism
Cartographer_Icons
Cartographer_Icons_GathererPack
Cartographer_Icons_MetaMapPack
Cartographer_Import
Cartographer_InstanceLoot
Cartographer_InstanceMaps
Cartographer_InstanceNotes
Cartographer_LookNFeel
Cartographer_Mailboxes
Cartographer_Mining
Cartographer_Notes
Cartographer_Noteshare
Cartographer_Opening
Cartographer_POI
Cartographer_Professions
Cartographer_QuestObjectives
Cartographer_Quests
Cartographer_Stats
Cartographer_Trainers
Cartographer_Treasure
Cartographer_Vendors
Cartographer_Waypoints
Cartographer_ZoneInfo
CharacterProfiler
ChatMOD
ClearFont2
ClearFont2_FontPack_1
ClosetGnome
ClosetGnome_Mount
ClosetGnome_Zone
DamageMeters
DetachedMiniButtons
eCastingBar
ElkBuffBars
Enchantrix
EnhTooltip
EQCompare
ErrorMonster
FishingAce
FlightMap
FluidFrames
FuBar
FuBar_BagFu
FuBar_BattlegroundFu
FuBar_ClockFu
Fubar_DamageMetersFu
FuBar_DPS
FuBar_DurabilityFu
FuBar_ExperienceFu
FuBar_FactionsFu
FuBar_FriendsFu
FuBar_GuildFu
FuBar_HonorFu
FuBar_ItemBonusesFu
FuBar_LocationFu
FuBar_MoneyFu
FuBar_MonkeyQuestFu
FuBar_NameToggleFu
FuBar_PerformanceFu
FuBar_PetInfoFu
FuBar_RegenFu
FuBar_SkillsPlusFuLt
FuBar_tcgTradeskills
FuBar_ToFu
FuBar_TopScoreFu
GFW_AdSpace
GFW_FeedOMatic
GFW_HuntersHelper
Grid
GridSideIndicators
GuildProfiler
Informant
ItemSync
LinkWrangler
MetaHud
MetaHudOPT
MobInfo2
MonkeyBuddy
MonkeyLibrary
MonkeyQuest
OneBag
OneBank
OneRing
OneView
Personal Sentry
Postal
QuestHistory
sct
sctd
sctd_options
sct_options
SimpleCombatLog
simpleMinimap
SmartBuff
SmartDebuff
SpamSentry
SpamSentry_bot
SpamSentry_report
SpamSentry_rp
SpellAlertSCT
SpellAlertSCT_options
Stubby
TinyTip
TinyTipExtras
TinyTipOptions
TrinityBars
XLoot
XLootGroup
XLootMaster
XLootMonitor