Arena Mods

Gladius v3

Gladius adds enemy unit frames to arenas for easier targeting and focusing. It shows a health bar, a mana bar below the health bar (optional), a cast bar below the mana bar (optional), a class icon to the left side of the health bar (optional) and important buffs and crowd control durations (optional, overlays the class icon). The frame resizes itself to the current bracket (optional).
Config: /gladius ui
Curse

Battleground Mods

AlarBGHelper 6.0.2

Battleground timer and coordination mod. Features: Auto release; Mini Map tooltip colorizing with class and race (if you have some tracking ability); Resource tracking. Nodes or bases status is shown in a compact frame. Clicking on a base name will: Left-Click: says "Help needed at <base name>", Middle-Click: says "<base name> now safe", Right-Click: says "Massive inc to <base name>"; Shift-Left-Click: says "On my way to <base name>.Hold on".
Curse

BattlegroundTargets

Shows all battleground enemies. Simple 'Enemy Unit Frame' for battlegrounds.
Curse
Review: WoW Insider

BG Defender

BG Defender (Based on AB Defender) gives you a little movable window with buttons to announce the number of incoming enemies at the base you're defending in AB, EoS, AV and WSG. There are also buttons to call for help or announce the base you're defending is safe. BG Defender will automatically pop up when entering a battle ground and close after you leave.
Curse
Review: WoW Insider

Capping

Capping is a battleground timer mod with some extras. Current Features: All battlegrounds/arenas have start timers. Arathi Basin: Node timers/Final score estimation. Alterac Valley: Node timers/Auto quest turnins/Request sync from others with Capping. Eye of the Storm: Flag respawn timer/Flag carrier display/Final score estimation. WSG: Flag respawn timer/Flag carrier display with health percent. Battleground minimap: Rescale/Narrow mode to remove unnecessary map areas and save space/Hide border. Other: Port expiration timers/Queue wait timers/Scoreboard repositioning/Capture bar repositioning.
Config: /capping
WoWInterface

PvPness2

This addon provides useful battleground information through various bars and timers. When you enter a new battleground, a frame will appear in the middle of your screen. You can move this frame to wherever you'd like by clicking on the BG name and dragging it. If the game hasn't started yet, you'll see a timer to when the battleground will begin. You can also type /teamspy to see a list of the opposing team's players sorted by server name and colored by class. It's a handy way to check for premades or just see what classes you're going to face.To access options, type /pvpness gui or go to the AddOns tab under the WoW Interface menu.
Curse

REPorter - Battleground Map

Slim and readable overview of current battleground. Allows you to quickly send reports about the current position or any other on the map. Capture timers of all battleground nodes are tracked. Health of the gates is visible on Isle of Conquest and Strand of the Ancients. Winner estimator will provide you time left to end of battleground..
Curse, WoWInterface

Wintergrasper Advanced

Wintergrasper Advanced is a MOD for people who want to know the time on Wintergrasp without the hassle of going to the battlemage, the zone, or the map every time just to find out.
WoWInterface, Curse

Misc PvP Mods

DiminishingReturns

Diminishing Returns (DR) helps tracking your teammate and own diminishing returns on hostile players by attaching icons to unit frames.
Curse

HealersHaveToDie 6.0.2

Puts a big red cross over opposing players who are healers and rings when you hover or target a unit of the opposite faction who healed someone else during the last 60 seconds (can be configured).
Curse
Review: WoW Insider

LoseControl

LoseControl makes it easy to see the duration of crowd control spells on your character by displaying them in a separate cooldown icon onscreen. It's also compatible with any CooldownCount or OmniCC type mods that display a timer on top of the icon.
Config: /losecontrol or /lc
WoWInterface, Curse
Review: WoW Insider

RETTabBinder

RETabBinder will automatically change your tab key binding to only target enemy players when in PvP zones, and to target all enemies when not.
WoWInterface