Never posted anything like this before but I spent a good amount of time going over other "Best In Slot" lists and trying to find my personal one. Because I spent a good deal amount of time doing this, I figured I'd post it somewhere and share, even though there are a million of these floating around.
Things to keep in mind: I use the agility MM Spec (still favoring Armor Penetration on gear as the primary stat of choice though)
My Armory (for reference)
Head: T10.25 - 77 Arm Pen
Neck: Wodin's Lucky Necklace (BoE) - 38 Hit
Shoulder: T10.25 - 55 ArmPen
Back: Recovered Scarlet Onslaught Cape - 52 Arm Pen
Chest: T10.25 - 77 ArmPen
Wrist: Scourge Hunter's (Gunship 25) - 40 Arm Pen
Hands: T10.25 - 63 Hit
Waist: Nerub'ar Stalker's (Festergut 25) - 63 Arm Pen
Pants: Leggings of Northern Lights (Lady D 25) - 77 Arm Pen
Feet: Rock-Steady Treads (LW, easy but expensive) - 47 Arm Pen
Finger: Ashen Verdict - 59 Hit and Frostbrood Sapphire (Dreamwalker 25) - 60 Arm Pen
Trinket: Deathbringer's Will (Saurfang 25) - 155 Arm Pen and Mark of Surpremacy - 128 Hit
Stat Stick: Oathbinder, Charge of the Ranger-General (Lich King 25) - 115 Arm Pen
Ranged: Fal'inrush, Defender of Quel'thalas (Lich King 25) - 36 Arm Pen
Arm Pen: 77, 55, 52, 77, 40, 63, 77, 47, 60, 155, 46, 115, 36 - 900 constant
Hit: Neck 38, Hands 63, Finger 59, Trinket 128 - 8% hit by gear so you don't need to gem for it.
Note: The only "low" (Non T10) ilvl piece would be trinket. It provides 3% hit at the cost of a better trinket that would give roughly 3% crit. However, if you choose to go with an Armor Penetration spec, you would pick up the 3% hit in your talents and use an Armor Penetration trinket like Mjolnir Runestone or Needle-Encrusted Scorpion. Grim Toll also works but you would use a slightly different talent build.
Note: I didn't list 25 man heroic gear because I won't be doing those for a while (my guild is currently 8/12 in 25 man and on Monday we will be 9/12 :) but all the gear in 25 man heroic is the same gear as 25 man non-heroic but with better stats.
16 hours ago