I don't think there are enough witches in D&D. There, I said it.
Witches are a fairy tale staple; and malevolent magic-users of both genders populate sword and sorcery fiction. Yet usually we see the 'sexy sorceress' more often than we see a nice, scary crone. Over the years, I've had PCs deal with plenty of evil wizards, but very few witches, and I don't have a good explanation for that. But I do have a solution.
Random Tables for Striga Generation
Why 'striga' and not 'witch'? No deep reason. The striga of folklore seem to exist in this space between life and death; they aren't just "evil female spellcasters" with an optional "rural" template overlaid. The entries in these tables go for a weird horror/fairy-tale vibe, as you'll see.
The options in the tables could randomly give you anything along the witchy spectrum (including a green-skinned witch with a broom), out to something truly weird that wouldn't be out-of-place in a game with a strong horror feel. The whole thing is system-less and meant for inspiration, not stat generation. I think they might be useful not just for characterizing witches, but for adding gruesome details to the many 'hag' variants which populate D&D's history. Hags are underused, too. Let's see some hag love!