Arena Junkies - strategies, rankings, talents, macros, tools, and just everything arena.
Got Warcraft - PvP character builds.
Noxxic - Gives average dps on the class as well as build glyphs gems rotation info and build and some tips on key binding.
- The Addons and Customization section for sites with helpful addons for PvPing.
- The How-To on using Ventrilo (a.k.a. "Vent"), which is required for guild PvP.