Smiral said
If you're into sludge, Melvins is always a good starting point. I would also suggest The Ocean and Mastodon. I feel like you're probably more a fan of the experimental/noise aspects however, in which case I would suggest Big Black, Jesus Lizard, Helmet, and White Zombie.
Tool and SOAD share alternative metal elements, so for that I'd suggest Faith No More, Jane's Addiction, Soundgarden, Rage Against the Machine, Primus, basically anything that was popular in the early 90s.
Love you Smiral, you're a legend. Thank you for adding a whole 15 hours of new music to my iTunes library.
Melvins are amazing, downloaded one of their albums (Houdini).
The Ocean, downloaded Pelagial and Anthropocentric. Cool stuff.
Mastodon was okay, not really my thing. Not that I didn't like it, just not bad, but not really good either
Big Black and Jesus Lizard weren't particularly great either, passed on both of them.
Helmet is super cool, downloaded their first four albums (Aftertaste, Betty, Meantime, Strap It On).
White Zombie, really like them as well. Grabbed Astro Creep: 2000 and La Sexorcisto Devil Music Vol. 1
Skipped almost everything in the second paragraph of yours, sorry. Like those bands, just not really enough to put em' in my iTunes.
That being said, I did in fact download Tool's entire studio discography.