For raids, you can check
http://ddowiki.com/page/Help!_Am_I_Raid_Ready .
Quest wise, after level 12 or so...
Lordsmarch Plaza Quests - Diplomatic Impunity -> Frame Work -> Eyes of Stone. You can't do these in any other order the first time.
Lordsmarch Plaza Part 2 - Quests can all be done in any order, including the end quest (Entrance can be selected without having done blockade busters/Assault on Summerfield/Undermine)
Gianthold Tor - Requires having done Madstone Crater, Prison of Planes, and The Crucible
Litany of the Dead - Requires completed sigil (see Am I raid ready under Abbot)
Harbinger of Madness - You should be able to enter "Into the flesh" even without having done the other 3 quests, however you won't get end reward or series credit.
Reign of Madness - Acute Delirium, Sane Asylum, and Lord of Stone may be required to enter Lord of Eyes.
Reavers Reach Stealer of Souls requires completing Enter The Kobold, Prey on the Hunter, and The Monastery, as well as 3 gems from various explorer areas (See Am I raid ready above)
The Path of Inspiration (IQ1) - You don't need to specifically be on any of the quests to enter with a party.
The Dreaming Dark (IQ2) - Eye of the Titan is required to reach the island containing the remaining 4 quests, however you can enter any without having done any other quests in the series.