In America there are the Oz books, of course, though they in any case seem something of an outlier: did Oz spawn other good Stateside witches in the decades immediately following? In the UK, though, mid-twentieth-century witches (e.g. in John Masefield's The Midnight Folk , T. H. White's The Sword in the Stone , Ursula Moray Williams' Gobbolino the Witch's Cat  and Barbara Sleigh's Carbonel, Prince of Cats ) are generally malignant, as per tradition, and that tends to be the case into the 1970s, too: see for example the witches in Mary Stewart's The Little Broomstick (1971) (soon to be an anime feature, by the way, under the title, Mary and the Witch's Flower) or Diana Wynne Jones's Wilkins' Tooth/Witch's Business (1973). The first good British witch I can think of is in Nina Beachcroft's Well Met by Witchlight (1972), and even she is paired off against a bad one.
In a slightly different category are the good comedy witches. Oddly, there doesn't seem to have been much influence in Britain from the magic-in-a-modern-suburban-setting style of American sitcom, as in Bewitched, The Addams Family or The Munsters (all 1964), where the comedy comes from the incongruity of the modern - unless the boarding-school setting of Jill Murphy's Worst Witch series (from 1974) counts as such. In Britain, naturally, we're all about the comic incompetence, as with Murphy's Mildred Hubble and (though to a far lesser extent) Helen Nicoll and Jan Pieńkowski's Meg and Mog (from 1972). Both Mildred and Meg count as good, I suppose?
As for New Age/Wicca-inspired good witches, I'm not really aware of anything in Britain until 1990, when we get Monica Furlong's Wise Child (if indeed Juniper really is a witch - I'm not sure she identifies as such) - although in New Zealand Margaret Mahy had begun as early as 1984, with the Carlisle witches in The Changeover.
This is pretty much a top-of-the-head list. I don't want a baptismal curse, so tell me - whom have I neglected? Can you beat Nina Beachcroft in 1971? I'm sure you can.