Questions:
What are the essentials and your opinions of these bands and their albums (I have probably asked about a few of these in the past, so apologies):
Internal Void
Revelation
Oversoul
Solstice
Pentagram
Trouble
Internal Void's best album is Standing On The Sun, which is not impossible to find, but Unearthed is also very good and easier to find. I haven't heard the newest one.
Everything Revelation has done is brilliant stuff, I highly recommend them. One of the best in the genre. Their first two albums have been reissued recently, you should be able to find them at Hellride. Also check out Against Nature, made up of three of the Revelation guys. Everything I've heard from them thus far is brilliant. Go to one of those bands' pages on metal-archives and go to the Bland Hand Records website, you can download pretty much everything either band has done there before you buy. I'm most familiar with Appease and Descend/Much In Little from Against Nature though, so those are the ones I would recommend.
I still haven't heard Oversoul, but Doomcifer blows his load over them from what I remember.
Solstice is another one of the bands that I consider to be among the best of the genre. Everything is good, but New Dark Age really stands above the rest.
Pentagram is of course absolutely classic. I first and foremost highly recommend their first album, Relentless, and the two compilations of 70s material, First Daze Here and First Daze Here Too, but Be Forewarned is not to be passed up either. If you're really liking what you've heard, the other albums are good as well, but not quite as strong, and Bobby Liebling's vocals have drastically declined.
Anything off of Trouble's first 4 albums are a safe bet, though the first two are definitely the best.
Admittedly, I've been using Necuratal's doom list on the LotFP board as a guide. Cheers.
No problem, glad I could help.
EDIT: Are all Solitude Aeturnus albums worth getting?
I would say yes, though that's based on minimal exposure to everything past Beyond The Crimson Horizon. I've probably only heard those albums once or twice, but I remember them being enjoyable, nothing that would prevent me from buying them. The first two albums (especially the aforementioned) are generally considered their best though, from what I understand.