Cultes des Ghoules are about the only Polish band I regularly listen to, some of their stuff is essential for me. Their type of of occult, witching, simple and repetitive but not quite raw as balls black metal is something that seems very slavic or Eastern European to me.
Maybe it's just the subject matter. Will keep an eye on this thread to find more Polish bands.

Loads of good stuff mentioned for people interested in digging more.

Not mentioned yet.

Mysteries
Neasit (demo 95)
Xantotol ( for real early days BM)
Thors Hammer
Capricornus

From more recent times you gotta check out

BEYOND TIME.
Also....
Old Leshy
Wartodd
Diabolical Fullmoon

The current scene is really strong and loads of stuff coming out paying homage to the 90s.

Cultes Des Ghoules are my fave BM band in the last 20 years.
Have liked Saltus quite a lot, back in the day.

This thread inspired me to listen to HEFEYSTOS - "Vilce Sjen" again, great demo.

DRUDKH did a cover version for "W Krainie drzew" from that deno on a split album, deadly tune!

I'd love to see more per country threads like this. If anyone is knowledgeable about a particular country fire one up.

Chilean DM could be an option. Crow has been posting a few in the now playing of late.

Massemord's "The madness tongue devouring juices of livid hope" MLP is the best thing to come out of LTWB collective (meaning pretty much interchangeable personnel between projects such as Furia, Morowe, Wędrujący Wiatr) and therefore the best "new" BM  to come out of Poland. I couldn't recommend it strongly enough.

Furia's "Marzannie, Królowej Polski" is deadly but I guess it looses a lot of its charm in translation, as the lyrics are close to phenomenal and they  play a big part in reception of this album for me.

For old school, raw stuff harking back to "the days" but not exactly original I'd recommend Szron's "The Puryficaticng flame of annihilation".

Also, as mentioned in some previous post, old albums of Behemoth rule. Even up to "Pandemonic Incantations" they had something unique going on.

Graveland following the voice of blood on today .what a weird album .

Jangly strumming for riffs ,out of time drumming and grim monotonous croaks for vocals .love it though.