Lady Malys was one of those HQ's that I originally did not like much. In fact I really thought of her abilities as second rate, although her background was kind of cool. After getting some games in though I was quick to find a dedicated purpose for her.
She is was banished from Asdrubael Vect's court which she didn't take well. Got pissed off, and flew into a violent rage. She flew off in all pissy into the webways where she met a half-real creature and won a contest of wills where the prize was the other's heart. She won, and when the creature vanished, it left behind a strange blade that moved on it's own, and of course it's crystal heart. Being the rational woman she is, she used the blade to cut out her own heart, and place the crystal heart into her chest. Slowly she regained her position as Archon of the Poisoned Tongue Kabal. The rest you can read about in the codex, but if you need a crazy overly dramatic, possibly demonic, woman in your life, her she is.
She is very reasonable for her points. She comes with a good Archon stat line. WS7 BS7 S3 T3 W3 I7 A4 Ld 10 Sv5+. It wasn't until the first time I fielded her during that first close shooting phase that I figured out she doesn't come with a gun. Not even a splinter pistol. Doesn't matter, but it was still odd, and probably something Phil Kelly just missed. However she really doesn't need one. She comes with plasma grenades, a steel fan (close combat weapon), The Crystal Heart, and the Lady's Blade. Her special rules are fleet, night vision, power from pain, independent character, invulnerable save (4+), and precognisant.
Her Crystal Heart makes her and the unit she is with completely immune to psychic powers. This is cool. If you have a unit you are concerned about losing (like an expensive death star unit), have her join it, and all those tricky psychic powers will do nothing to your unit.
The Lady's Blade. This is very similar to a Djin Blade. It is a power weapon, gives her two bonus attacks a round. However if these extra attacks roll doubles, they do not strike the wielder, they simply miss and do not get anymore bonus attacks the rest of the game.
Precognisant. After both sides have deployed at the start of the game, the eldar player may redeploy D3 units in his army, including placing them in reserve.
In close combat her strength is her biggest limiting factor. S3 is tough, however she does get 5 attacks with her extra close combat weapon and an additional 2 with her Lad'ys Blade. This gives her 8 possible attacks on the charge at S3 at I7 (S4 I8 with a second pain token). Even though she is good in close combat, that is not where her skills come into play. Her cyrstal heart is wonderful added to a unit of incubi or other unit you do not want to get messed with when facing psychic powers (and everyone but Dark Eldar have them).
Incubi is where I generally have her, standing right next Asdrubael Vect. With Vect able to seize initiative on a 4+, her ability to redeploy units gives you that Fu to your opponent. He is damned if he lets you go first (your army should be designed to go first) since you can re-deploy, and damned if he goes first and you seize the initiative. Since I've found that after the first time people see Vect's seizing the initiative power, they always go choose to go second, Lady Malys really pushes that advantage of redeploying a couple key units (on average) so that you get some serious advantages during deployment. For opponents, it's best to reserve your army against this combo. Although most armies lose their advantage at this point and can come in piecemeal.
Since figuring out how much this messes with 80-90% of the people I play against, I really like Lady Malys and Vect paired up. Of course you don't have any pain tokens at the beginning of the game, just go get them. In other lists, her redeploy is nice and 50% of the time it will really come in handy. It allows you to place your assault units where you really want them so that you can get that first round assault where you need it. Deployment is a huge part of the game, and Lady Malys simply takes advantage of it.
Now the question remains, "What model do we find for her, or do we wait to see what GW comes up with?"