I like the idea of variant patrons. For instance, warlocks sworn to Old Testament angels --who are scary as all get-out. The traditional way to swear an angel-pact, BTW, is to attempt to wrestle an angel to the ground. If you win, the angel dislocates your hip and tells you a secret. The secret is the angel's name. The angel's name is it's bond. Presto, you are now a warlock! (and you get to append -el to your name, and forevermore walk with a limp).
Also, Job-as-a-warlock has potential. He swears a pact with Jehovah, who immediately sics Satan on him (to continually test his bond), but Job remains faithful/loyal and everything works out in the end (except for Job's original family).
Ahem... as for custom Patrons in my campaign, we have two at current count.
The Petitioners are sworn to unnamed (and unnamable?) forces from the far shore of the Astral Sea. They might be Great Old Ones, they might not. They're unusually interested in mortal affairs, but there aims are unclear. What is clear is the Petitioners run a magical racket. Almost like Mafia fixers. People 'petition' them with money, in the hopes the Petitioners will fix their problems, usually via harming someone. If a warlock tries to break their bond and leave the employ of the Petitioner's Hall, they get a visit from Mr. Gladmarrow -- a humanoid figure covered in bony spines who favors wearing top hats. He might be the patron. Or just hired muscle. Anyway, he liquefies the bones of the warlock who wants out, and then drinks them up (just the bones, not the flesh).
The Pig Pact Warlocks are sworn to the Great Treasure of Heaven, a giant dire boar sow who might be a goddess (and a Socialist). Then again, she might not. Miracles have been performed in her name, and many goblins worship her, but the ecclesiastical jury's still out. One of her most consistent & well-documented feats is the ability to free Petitioners from their pacts by somehow scaring away the aforementioned Gladmarrow.