I love the album Decipher by the Dutch band After Forever. All their other work is quite lame unfortianetely. Also Dutch band Within Temptation with their album Enter is kind off OK but wouldn't really listen to it.

Decipher is strong and has a heavier male voice next to her singing. I never found any other bands playing this style that appealed to me and I've tried alot.

Maybe someone here knows some good ones!

I have only ever heard their self titled, but I LOVE symphonic/gothic metal, so il try to come up with something

Sirenia - at sixes and sevens. really heavy, excellent with both vocalists putting in an excellent performance.

the gathering - mandylion. I need to say this in every thread, perfect album

ashes you leave - songs for the lost. i prefer desperate existence, but that album fits the bill a lot more.

and just in case you don't know the fantastic tarja era nightwish, try their album oceanborn.

in case you dont know epica try some stuff by them. they're not as good as AF but they are ok.

Within temptation really improved after enter, black symphony is excellent.

leaves eyes - vinland saga. not particularly heavy, but lovely. their male singer is awful, but he shuts up most of the time, thank god. Njord is heavier, but the production seems off to me

lacuna coil - the eps, in a revirie and unleashed memories. these albums by them DIDNT suck, but the male vocalist does clean vocals

theatre of tragedy - aegis, and the heavier first 2 albums are shining examples of quality gothic metal.

estatic fear - doomy gothic metal, but one of the most innovtive bands ever

delain are very poppy, but maybe youll like lucidity. Most of april rain is a bit sugary sweet though

tarja turunen's solo project is a lot better than i expected

tristania are suposedly one of the best gothic metal bands ever, but i dont see too much in them tbh

If you really like the REAL gothic stuff, depressing lyrics and atmosphere then go no further than draconian and Nox Aurea. Also My dying bride, but they only have male vocals

the 3rd and the mortal - tears laid in earth, laid back and a bit long, but really really good.

the sins of thy beloved, much better than tristania, who i never understood the hype for, these guys and gals really know what gothic metal is all about

You might like Vanguard (Nor)

I'll second At Sixes and Sevens by Sirenia. I'll also second Epica because they use growls and female vocals but they can be hard to get into sometimes.

Also, I'd recommend you ignore Nightwish, The Gathering, Tarja Turunen, My Dying Bride and Delain since they aren't what you're after (they don't have growled male vocals with female vocals). Tarja's solo material sucks anyway, its just pop with metal riffs thrown in randomly.

I'd recommend you try Luna Obscura from Greece, they use growls and female vocals.
MA Page: http://www.metal-archives.com/band.php?id=39445
Sample: http://www.youtube.com/watch?v=_VwPcWWKzbA

Catafalque might be what you're looking for, they use growled and clean male vocals along with female vocals. Only their first album is good though, the second sucks.
MA page: http://www.metal-archives.com/band.php?id=3942
Sample: http://www.youtube.com/watch?v=EHu-lz_-4Io

Darzamat, perhaps? Female vocals and growled male vocals.
MA page: http://www.metal-archives.com/band.php?id=2129
Sample: http://www.youtube.com/watch?v=a3FD_E-9HxA

Elnordia is also worth a try. Growled male and clean female vocals.
MA page: http://www.metal-archives.com/band.php?id=100666
Sample: http://www.youtube.com/watch?v=xBx4syzycdw
(Don't go to Elnordia's official site or Myspace, I got a malware warning last time I tried).

Trail of Tears is another; try their newest album which uses growled male and clean female vocals.
MA page: http://www.metal-archives.com/band.php?id=1236
Sample: http://www.youtube.com/watch?v=SL2RoDXIiiI

And finally, Thalarion, who use growls and female vocals also.
MA page: http://www.metal-archives.com/band.php?id=3332
Sample: http://www.youtube.com/watch?v=uRzZmlJvII8

Sorry if I've overloaded you with recs, but there are plenty of good underground gothic metal bands much better than many of the more well-known ones.

I didn't like anything from the Youtube links

It's all too slow / weak for me, I do need some power in the music!

OK, no problem. Was worth a try. What you could do is search "gothic/power" in the genre box of the advanced search. That would give you a list of all the gothic/power metal hybrid bands (like After Forever), and you'd just have to use youtube and myspace to find the ones that have growls as well as female vocals. It might take a bit of effort but you should be able to find something you like.

you need to hear meridian by sirenia.

Yeah I know but I always ask a forum as well since you just might find some gems. I always use LastFM similar artists but in this case I don't like any of them...

Sirenia was in the right direction but not my taste.

Yeah, the Lastfm similar artist thing has been largely useless in my experience. I'd still recommed trying Epica since it was founded by the main creative force behind old After Forever.

If you haven't already, try this song: http://www.youtube.com/watch?v=uYhyKSl59Q8