If anyone wants help setting up and customizing and of the following mods (all of which I highly recommend), let me know:
Bartender4 (custom action bars)
Shadowed Unit Frames (custom frames for self, target, target of target, etc.)
Grid+Clique (great raid frame replacement, especially for tanks and healers, with Clique being good for fast setup of mouseover macros)
Augmented Virtual Reality (helps with raids tremendously by highlighting key areas to take note of, such as where malleable goo is going to land on Professor Putricide)
PowerAurasClassic (tracks buffs, debuffs, cooldowns, and many other things... highly customizable)
Mik's Scrolling Battle Text (replaces the on-screen battle text with less-cluttered and more informative battle text wherever you choose on your screen, and also tracks power gains, buffs/debuffs, and cooldowns)
Omen3 (threat information, especially important for tanks and dps)
Quartz (casting bar replacement, highly recommended if your class has any spells with a casting time)
RatingBuster (shows you what stats you get out of gear/items, including after taking into account buffs/talents)
TidyPlates+Threat Plates (nameplate addon that gives you more information while looking less obnoxious... especially recommended for tanks)
Titan Panel (small panel on the top and/or bottom of your screen that displays a wide range of information, such as gold on account by character, durability, framerate, latency, bag space, mana regen, and many more bits of information through additional addons)
DeadlyBossMods (tracks key events in raid and dungeon encounters... everyone who raids should have this)