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 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.