Patch day 9/25
Many of these mods have not been updated for 2.2 as of yet. I will keep checking and post changes as I find them.

Required Mods — Updated 9/25/2007

• KLHThreatMeter
  Guage your aggro against the main tank.

— Updated 2.2

• CT_RaidAssist — Updated for 2.2
  Many raid functions, also an improved Raid unit frames over the blizzard one.
• Deadly Boss Mods — *beta* Updated for 2.2
  Alerts and timers for boss/pvp events. This helps you time the various phases of the raid.

Recommended Mods — Updated 9/25/2007

• AtlasLoot Enhanced
  Find info on phatty loots from any boss/profession, and link it in chat.
• Cartographer — UPDATED for 2.2
  Tons of map functionality, including always seeing your guildies location, points of interest for professions (mines, herbs, fish, etc.).
• Recap (Hawksy)
  Damage/Healing report, very configurable, though memory intensive.
• X-Perl UnitFrames — UPDATED for 2.2
  Party/Raid/Player unit frames with added functionality over CT and others. This shows you who has agro, what buffs/debuffs, their distance to you, also party targets and is highly configurable. An alternate recommendation would be AGUnitframes, and although more configurable, lacks some features like party targets, grim reaper, raid monitor and psuedo-main-tanks and is behind in development at the moment.