The album I´ve been listening to most frequently (about 1,200 times until now) and which has always made it into the top 10 of my yearly playlists since I bought it 1991 is Fear Of God´s "Within The Veil". Though I don´t listen to it as often as I used to in the first years after its release, I still love it as much, especially Dawn Crosby´s (R.I.P.) vocals, which to me are some of the most impressive I´ve ever heard, but I like this album in any respect, not just vocal-wise.
My unrivalled no. 1 since April 2002 has been "Terrestrials" by Atrox - within the rather short period of two years it got about 400 spins and though I won´t continue to listen to it as often as I´ve done so far (because there are always some new albums to which I usually listen more often than older stuff - at least in the first few months
), it is very unlikely that I´ll ever get bored with it, because just as "Within The Veil" I like this one in any respect as well and there´s so much to discover!
Another (more recent) album I still haven´t got enough of is Nightwish´s "Oceanborn".
As far as older albums are concerned, "Suffering Hour" by Anacrusis is one of the albums I´ve been listening to most consistently since its release, as well as Znowhite´s "Act Of God", Détente´s "Recognize No Authority" and Voivod´s "Killing Technology".
And finally, some of the "oldest" albums I still like (nearly) as much as when I listened to them for the first times (though I listen to them very rarely now) are Metallica´s "Ride The Lightning" (it sort of started it all for me) and Fates Warning´s "The Spectre Within".
Well, there are lots of other albums from the late eighties/early nineties that I still like and listen to (occasionally), but sometimes it might take some years until I rediscover them - and wonder why I haven´t listened to them more often.