This is a BiS list for a Shadow Priest in PvP. D2 is obviously better, but this should get you started as you work your way up.
Head:
Crimson Felt Hat - Spellweaver's Turban
Neck:
Orb of Darkmoon - Amulet of the Dawn
Shoulder:
Thuzadin Mantle - Deadwalker Mantle
Back:
Deep Woodlands Cloak - Frostwolf Advisor's Cloak
Chest:
Robe of Everlasting Night - Robe of Winter Night
For PvP I prefer Flarecore Robe
Wrist:
Rockfury Bracers - Sublime Wristguards
Weapon+OH:
Verimonde's Last Resort - Tome of Shadow Force
Wand:
Ritssyn's Wand of Bad Mojo - Bonescreeper Stylus
Gloves:
Felcloth Gloves - R7 gloves
Belt:
Frostwolf Cloth Belt
Legs:
Bloodvine Leggings - Flarecore Leggings
Boots:
Maleki's Footwraps - R7 boots
Rings:
Maiden's Circle - Advisor's Ring
Trinkets:
Briarwood Reed - Mindtap Talisman - Draconic Infused Emblem
D2 Set Items Total:
Spell Dmg......120
Hit %..................0
Intellect...........115
Spirit................96
Stamina..........108
MP/5.................21
Crit %.................1
Also: Auto-Shield (350), +8 all resists
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