As I'm sure you can tell, I enjoy fantasy, and fantasy books tend to be full of magic-workers. I tend to prefer the books where magic is more of a practical thing than a spiritual one. For instance, I always thought it was stupid when people criticized the Harry Potter books for promoting non-Christian religions, when magic in that world doesn't really appear to have a religious component. In the Discworld books, there are a few statements that say that witches and wizards are well aware that gods exist, but they don't see the need in actually BELIEVING in them. Of course, all fantasy universes are different, which is why, for instance, gnomes can be garden pests in one series, tiny warriors with Scottish accents in another, metal-and-jewel-mining rock fairies (and spelled without the G) in a third, and inhabitants of a land deep underground where you can get juice out of a ruby in a fourth. Overall, though, I get a picture of witches being largely homespun magicians who work with herbs and such, while wizards are book-learned and scientific in their approach to magic. Traditional gender roles dictate that the former is usually female and the latter typically male, but I don't see why this would be strictly necessary. Terry Pratchett's Equal Rites deals with a girl's challenges in enrolling in a school for wizards, although The Colour of Magic suggested that countries elsewhere on the Disc already had female wizards. I believe there's some historical precedent for "witch" and "wizard" being gender-specific terms for the same sort of person, but it doesn't really seem right to me.
So what IS the appropriate term for a male witch? Maybe there doesn't need to be one, as both men and women were accused of witchcraft in the past. As a kid, I asked my dad what a male witch was called, and he said they were warlocks. That largely works, although there's more of a negative connotation for that word (it literally means "oath-breaker" or "liar"). As for female wizards, I've seen the term "wizardess" used before, most notably at the beginning of The Land of Oz: "Mombi was not exactly a Witch, because the Good Witch who ruled that part of the Land of Oz had forbidden any other Witch to exist in her dominions. So Tip's guardian, however much she might aspire to working magic, realized it was unlawful to be more than a Sorceress, or at most a Wizardess." This seems to imply that a wizard/wizardess is more powerful than a sorcerer/sorceress, which is kind of odd. It seems to be the general rule (at least in what I've seen, which admittedly is only a small fraction of all the stuff written about magicians) that, if a wizard and sorcerer are being ranked, the latter is the more powerful one. That even seems to hold true for Oz, where the most powerful magic-worker is the Sorceress Glinda. But then, Glinda was originally called a witch, so we can see that L. Frank Baum was pretty loose with these terms. I think the point of that passage isn't so much to rank magic-workers as it is Mombi trying to find a loophole in order to practice her witchcraft. We see much the same thing in Ruth Plumly Thompson's The Purple Prince of Oz, in which Ozwoz claims that the laws of Oz don't address his form of magic, wozardry. Anyway, while "wizardess" seems valid enough to me, -ess endings to denote femininity have been falling out of favor as of late (actress, waitress, stewardess, etc.). So I don't see why a magician like the book-smart, scientifically-minded, modern-thinking Hermione Granger wouldn't just go ahead and call herself a wizard, instead of a witch. But I guess it's mostly just semantics.