Seed of Corruption

Quite the interesting spell. Some facts; SoC’s explosion will not damage the original target of the spell, only targets around it. SoC’s explosion itself doesn't count toward towards the 1044. SoC’s explosion can crit and benefits from +spell damage. This is an excellent spell, if used properly. Let me give some examples; PvE: Put SoC on a number of mobs (try loading up 3-4 targets that aren't being attacked to avoid premature explosions), and watch the numbers fly. PvP-wise, Putting it on someones pet lead to an amusing effect. SoC can do great damage in a PvP crowd, provided it goes undispelled. It can be a nice little farm tool for low level mobs as well. This spells uses are many, it's easily one of my favorites.

Fel Armor

Well, this is a really nice upgrade for warlocks in the expansion. Fel Armor will replace Demon armor 99% of the time. Just the spell damage definitely would’ve been enough to give up demon armor, but the additional 20% (26% with Demonic Aegis) healing received makes the choice even easier. The extra healing works with drain life, siphon life, bandages, healthstones, healing potions, bandages, and any heal or regen other people cast on you. It’s simply awesome.

Ritual of Souls

This one helps to diminish the headache of handing out healthstones (and collecting the shards for em) on raids. It’s useful in 5 mans and pvp as well though.
Ritual of Souls is an all around good utility spell.

Soulshatter

As the aggro reducing abilities of warlocks are a little limited, this is another very welcome addition. The cooldown may be on the high side, and the spell can be resisted by mobs, but Soul Shatter is far better than the warlocks” previous aggro reducing spells. (there are none)

Incinerate

A good fire nuke. Searing Pain has always been usable, but the additional threat is a problem in PvE. Immolate can be used as a nuke, but at a high mana cost.
Incinerate makes for a nice alternative.