My multiboxing mods list (with minor differences between group types):



Items:
1 = Fubar_MoneyFu
2 = Fubar_DurabilityFu (shows durability of your items + auto-repairs at NPCs)
3 = PerformanceFu
4 = FarmerFu (shows how many of a particular item(s) you've farmed)
5 = AllPlayedFu (time played among all chars on this account)
6 = Vanas Kill-On-Site mod (tracks payback for later)
7 = BugSack (yay for no errors on screen!)
8 = RegenFu (Mp5, etc.)
9 = SoulJarFu (helps track your soulstone buffs; compliments CT_Buffmod nicely)
10 = QuestsFu (watches quest completion for whole group. VERY nice for boxers)
11? = All the 11s are Pitbull unit frames; very lightweight in terms of CPU and resources but feature-rich.
11a = Focus
11b = Self, group and partypet bars (all completely configurable)
--- Note that Donrafael has aggro here
11c = partytarget and pettarget bars
11d = Your target and your target's target
12 = XP Gain Notify
13 = IceHUD (like ArcHUD but fewer bugs and less overhead)
14 = Omen (like KThreatMeters but with MUCH less overhead)
15 = CT_BuffMod (shows bars plus plays audibile alerts when buffs are expiring)
16 = Mr. Plow (rearranges/stacks/sorts your inventory and bank)
17 = MiniFriends

Some others that aren't listed but that I use regularly:
--> OmniCC (big, bright flash on a button when the cooldown timer is up)
--> Atlas mod set for maps and instance loot tables
--> Auctioneer
--> AuctionFilterPlus (sorts AH list by full stacks, buyout only, etc.)
--> AutoAcceptInvite
--> AutoProfitX (automagically sells gray trash loot and specified others)
--> Cartographer (teh awesomeness)
--> Clique (Easier to config than Healbot and turns Pitbull Unit Frames into Healbot on steroids. Can't live without this now.)
--> CT_Core, CT_ExpenseHistory and CT_MailMod
--> DeclineDuel
--> Enhanced Flight Map
--> Enhanced ToolTip
--> EquipCompare (compares loot to your equipped items)
--> FreeRefills (auto-buys food/water/reagents that you specify)
--> Fubar (ACE2 bars like TitanPanel; much less overhead)
--> SpeedFu (speedometer for WoW)
--> Fizzwidget's TrackMenu
--> Customized version of "Headshot" mod; plays sound when one of my guys lands a crit; makes watching aggro a bit easier
--> Igor's Mass Auction (nice for spamming auctions)
--> LevelSnap (screenshot on ding)
--> LightHeaded (puts WoWhead.com quest info into your quest log!)
--> MobHealth2 and MobInfo2 (remembers info about your NPC kills)
--> OneBag (ACE2 bag consolidation mod)
--> Reslack (autoaccept rez/summon)
--> SCT/SCTd (modified scrolling combat text)
--> SellValue (remembers how much stuff sells for and puts it into tooltip)
--> SimpleRaidTargetIcons (radial selection for raid/group target markers)
--> SpellAlertSCT (warns when enemy casts spells)
--> SuperMacro (many macro enhancements)
--> ThreatToKTM (sends Omen threat meter data to people who have KTM but not Omen)
--> TinyTip/TinyTipExtras/TinyTipOptions (smaller, more better unit tooltips)
--> TomTom (allows LightHeaded to set map waypoints with on-screen direction arrow from WoWhead.com coordinate data)
--> WoW Instant Messenger (pops up IM-style dialogs for /whispers and tracks /whisper history)

Now, all that (because the ACE2 framework is so well done) only uses about 30-35MB of UI memory. Start up another thread or PM me if you have any questions about configuring any of these or how any of it works.