Warbringer
Explorer
I always liked the idea of the warlock...unfortunately I never liked the execution. My fave warlock so far has been the one in the 5e playtest one, so here's hoping they get it right this time.
In my B/X campaign, I made the warlock an alternative class for the cleric, since they're very similar. The cleric worships greater powers; the warlock makes deals with them.
In both cases, I changed the spellcasting mechanic to a reaction check. You had to convince the greater power to make whatever spell you wanted to happen, and you might have to power it with your own, or anothers, energy (hit points).
The 3e warlock was good, as it was so different form mages at the time... I'd love to see this as feat tree or something that is magical power without learning or innate ability.