There have been numerous versions of the Witch class over the years. The one I remember the most was from Dragon 114, which also caused a bit of an uproar due to the provocative nature of the cover art. That was a Witch for AD&D and while interesting I thought it was a bit too much. Like most things in AD&D to be honest. I liked the idea, but not the implementation.
The character classes in Tom Moldvay's edit of D&D are a great model to emulate. Ranging from only a quarter page to a half a page in length they are concise, yet evocative. Pages of mechanics are eschewed in favour of a few details. I like this approach very much.
Here then is my take on the Witch, usable in various OSR versions of D&D, Swords & Wizardry, Labyrinth Lord, LotFP, etc. This is not a new age crystals and potpourri witch. This is the Witch of folklore, black magic, and pacts with devils.
UPDATE: The Witch Class PDF has been updated with the excellent illustration by Catherine Mason (see below). The 1st version with the John William Waterhouse painting is also available.
Pagan in Skyclad by ~Liabra on deviantART