Considering the prominence of women as Archmages in Warcraft is perhaps more a reflection upon Dalaran than it is anything else, since being named an "Archmage" is a title very specific to prominent members of the Kirin Tor ~ literally, the magocratic governing body of Dalaran. It is mostly political in nature, though it does generally allude to great arcane power as well. As such, Archmages would typically be limited to humans, gnomes and high elves ~ though in WoW currently, only humans are typified as representing Dalaran's leadership in almost every case with prominent exceptions lying amongst the undead, who were afterall once human too and usually also (former) members of the Kirin Tor (ie. Kel'Thuzad) and even then the vast majority of them are men. Blood Elves seem to have their own power structure now, removed completely from Dalaran with titles such as "High Nethermancer" or "High Astromancer" and trolls... well, they're so old, they've never really had any need or use for an orgization like Dalaran. They probably view it as the silly political mess that it is.
A. Lady Jaina Proudmoore
When talking about women Archmages, you would typically only be talking about one person... and that is Jaina Proudmoore. She is the Queen Bee, not only of Theramore or of modern Azerothian women mages but to some degree, of the Alliance as a whole, arguably. Where she lacks in terms of actual armies and people she more than makes up in terms of her aristocratic influence (not only in the Alliance, but the Horde as well) and impact on the recent history of Azeroth. She represents a true figure of leadership amongst the human race, whereas Bolvar in Stormwind isn't a true ruler and the King of Stormwind is... a kid. Not only a prominent member of Dalaran's Kirin Tor magocratic body, she is also of royal lineage to the Island nation of Kul Tiras (which is not currently in WoW, yet) ~ essentially a "Princess" of that nation (placing her in highly influential positions of no fewer than three Alliance "nations" ~ no small feat). Not much in game currently alludes to her true influence over Azeroth short of the coming Battle of Mount Hyjal in which she plays a prominent role, with only one less noteable exception being during "Children's Week" when your orphan asks you to take him to get her autograph ("They say that Lady Jaina Proudmoore in Theramore is one of the greatest heroes the Alliance has ever had. When I grow up, I wanna be a hero of the Alliance too!"). Don't be fooled! When you get her autograph, keep it for yourself! ;)
Apparently, in Mount Hyjal her towering presence is quite literal, as I hear she's literally like 10 feet tall. But it isn't even that different from her embodiment in Theramore. If you go back to her there sometime, take note ~ she is as tall as a night elf, if not a little taller! She is also an "Epic" quality/rarity card in the Warcraft TCG, which I am proud to say I received from Zanzola as a birthday present (even though I've never bothered to actually play the TGC). :D
B. Archmage Angela Dosantos
Angela is probably most noted as the "Watcher of Atiesh" and a member of the Brotherhood of Light, the secretish sect of the Argent Dawn associated with combatting Kel'Thuzad. In game terms, she is the person who provides attunements for entrance into Naxxramas and can be found perpetually embroiled in the planning and debating taking place in Light's Hope Chapel. Sadly, her days of prominence in WoW were short-lived, but I still remember you Angela!
C. Archmage Leryda
A high elf Archmage! A first that I can readily think of in WoW. Sadly, not much more is known about her, since not much is known about the Violet Eye in general. Granted, it's a "secret sect" (much like the wizards of Dalaran seem highly predisposed towards forming), but really... they seem little more than a tacked on quest line and as such, I sadly don't find them too compelling personally.
Maybe you know who she is and maybe you don't... since frankly, if you've never levelled a mage or warlock, there has never been a reason to even know that she exists... Buried deep in Dustwallow Marsh, Tabetha is a hermit who lives in a shack not too far from Onyxia's Lair, far off any well travelled path and very close to areas that pose significant threats to players who would otherwise be trying to adventure there. While she is not an "Archmage" per se, attributable to her apparent lack of association with Dalaran or any other specific faction... the mage and warlock trainers of both Horde and Alliance know of her for some reason and they send you to her (more than once, if you are a mage), where she grants some fairly challenging quests. Fact of the matter is, this mysterious woman is a very powerful magician and everyone seems to know it.
So what's her deal, exactly?
There is no official answer, but I am a believer of a theory that she is in fact, Aegwynn ~ former Matriach/Guardian of Tirisfal, Mother of Medivh, which while not an "Archmage" exactly, implies someone much more ancient and powerful than a simple Archmage... she once vanquished Sargeras, the creator of the Burning Crusade afterall! :O So yeah, if Medivh's dad has kicked your butt recently, you seriously don't want to know what his mom could do to you... Aran was a simple court conjurer afterall (an insecurity he readily admits to during the fight in Karazhan. ie. "I am not some simple jester!", "Yes, yes, my son is quite powerful... but I have powers of my own!" Insecure much??) ~ Medivh's true power came from his mother. Aegwynn still lives in solitude somewhere, whether she is in game or not, and given that her most recent contact was with Jaina, it would stand to reason that Tabetha's proximity to Jaina in Dustwallow would support the idea that this simple hermit is someone much, much more powerful than is readily apparent.
"Honestly, they don't teach you young mages anything these days. Violet Citadel's gone to pot, and that's the truth." - Aegwynn (to Jaina)