my apologies for reviving a somewhat old thread, but...
if you go to the andy sneap forum on ultimatemetal the users there have amassed a particularly nice collection of samples that you can download for free.
this thread has most of them all on one page
if you search through the forum, however, people are adding new shit all the time. there's one in the meta thread that has a bunch of kick samples ripped from albums by all sorts of different metal bands, my favorite being the kick from blessed are the sick by morbid angel.
hope this helps. it's been a useful resource for me for a long while now...
Oh subjects of pain
Lovers of death
You will feel
The yearning flames