Deathspell Omega are probably one of my favourites as well. I say 'probably' and 'one of', because every time I try to make a list I suffer by having to leave bands out. I consider them to be one of the epitomes of Black Metal as their lyrics actually go beyond "Hail Satan" (repeat: 666 times). That makes them far more powerful and empowering than the easy-going nature of the more punk-based black metal.
Paracletus is wonderful. Personally, I think Si Monvmentvm is a bit easier to get into and the lyrics are easier to grasp. One of the things I appreciate is the fact that they're actually making proper use of the different languages instead of atrociously crooked latin etc. I'm still hunting SMRC on vinyl, but it's not that easy to get.
As to lyrics, I think you'll find Anaal Nathrakh actually have lyrics that go a fair bit deeper than they might at first glance. Dave Hunt studied philosophy and has a tendency to include a smattering of references. The titles, album titles and the understandable bits are the clues to go dig deeper.