Yeah, 2 levels in Warlock can be very fun.
Telepathy and communication with anything from lv1 onwards. Or temphp every time you kill anything (just Warlock level + Chamod, but still).
Hex spell has no save, and gets you extra damage on every hit, and you can bounce it from target to another on death.
Devil's Sight for never being hindered by darkness (regular darkvision still gets Perception penalties in the dark), even the Darkness spell.
If you have the Cha for it, Eldritch Blast + Agonizing Blast + Repelling Blast, for great ranged damage and control.
Lifedrinker to add more damage to your every melee hit from lv12 onwards.
At-will Hold Monster from lv15 onwards.
Not too tempting for the full casters (since 2 levels is more slots and an extra level of spell power for them), but for others (especially Paladin), it could be nice. Because hey, your non-caster levels aren't getting you much sweet stuff anyways.