The Beaststalker Armor Set pieces drop from Stratholme, Scholomance, and Blackrock Spire (Both upper and lower).

Belt: Drops off of various mobs in LBRS
Boots: Drops off of Nerub'enkan in Undead Stratholme
Bindings: Drops off of various mobs in Stratholme (Both Live and Undead side)
Cap: Drops off of Darkmaster Gandling in Scholomance
Tunic: Drops off of General Drakkisath in UBRS
Pants: Drops off of Baron Rivendare in Undead Stratholme
Mantle: Drops off of Overlord Wyrmthalak in LBRS
Gloves: Drops off of War Master Voone in LBRS

Also, the Belt, Bindings, and Gloves are Bind on Equip, whereas everything else is Bind on Pickup.
I hope this helps.

~Jerotin

at pre-tbc I had 7/8 of the set on my enhancment shaman, as its basically the only PvE dungeon set that enhancment shamans can use, was kinda funny when in groups i was told to put that aspect on to make the whole group run faster :P

The Beaststalker is the Hunter Teir 0 set. The current drop rates are as followed (got them all of www.allakhzam.com, and only did the best drop rate if more than one drop):

-Beaststalker's Belt = BRS ; Smolderthorn Headhunter ; 1.90 %
-Beaststalker's Bindings (Bracers) = Strat ; Crimson Defender ; 1.84%
-Beaststalker's Boots = Strat UD ; Nerub'enkan ; 12.24%
-Beaststalker's Cap = Scholomace ; Darkmaster Gandling ; 7.22%
-Beaststalker's Gloves = LBRS ; War Master Voone ; 9.32 %
-Beaststalker's Mantle (Shoulders) = LBRS ; Overlord Wyrmthalak ; 9.11%
-Beaststalker's Pants = Strat UD ; Baron Rivendare ; 6.58%
-Beastalker's Tunic (Chest) = UBRS ; General Drakkisath ; 5.88%

Cheers

This is the Hunter Dungeon 1 set, collected in 60th instances pre-tbc. They are used to upgrade to Dungeon 2, and the other sets are:

Magister's Regalia - Mage (Cloth)
Vestments of the Devout - Priest (Cloth)
Dreadmist Raiment - Warlock (Cloth)
Shadowcraft Armor - Rogue (Leather)
Wildheart Raiment - Druid (Leather)
Beaststalker Armor - Hunter (Mail)
The Elements - Shaman (Mail)
Lightforge Armor - Paladin (Plate)
Battlegear of Valor - Warrior (Plate)

REMEMBER: These don't have class restrictions. You can use any that you can, but the stats are tuned to the particular classes. You also require your class's set before upgrading to Dungeon 2.

As of Patch 2.0.1, all armor in the Beaststalker set carries + attack power. Some stat values that were on the previous versions of the pieces have been lowered.