Here you will find guides to reach bosses and boss strategies for 5 man instances as well as general information about each instance.

Howling Fjord:
Utgarde Keep (Level 70+)
Utgarde Pinnacle (Level 80)

Borean Tundra:
The Nexus (Level 71+)
The Oculus (Level 80)

Dragonblight:
Azjol-Nerub (Level 72+)
Ahn'kahet: The Old Kingdom (Level 73+)

Grizzly Hills/Zul'Drak:
Drak'tharon Keep (Level 74+)
Gun'Drak (Level 76+)

Dalaran:
Violet Hold (level 75+)

Storm Peaks:
Halls of Stone (Level 77+)
Halls of Lighting (Level 80)

Caverns of Time:
Culling of Stratholme (Level 80)