http://www.minecraftforum.net/topic/1969520-17-using-summon-give-datatags-in-map-making-tutorials/
Basically you can use commands to spawn in monsters with set Armor/Weapons(enchanted too), Potion effects, Name tags and much more.
Skeleton with full Protection V Diamond set with Sharpness V Diamond Sword(You'll have to edit X/Y/Z)
[code]/summon Skeleton X Y Z {Equipment:[{id:276,tag:{ench:[{id:16,lvl:5}]}},{id:313,tag:{ench:[{id:0,lvl:5}]}},{id:312,tag:{ench:[{id:0,lvl:5}]}},{id:311,tag:{ench:[{id:0,lvl:5}]}},{id:31:5}]}}]}[/code]
Want to make custom Villager shops too?
[video=youtube;VIWISsqbC9A]http://www.youtube.com/watch?v=VIWISsqbC9A[/video]
Thought I'd share this with you guys.