While it's popular to refer to various commercial nu metal and emo bands (as well as some non-commercial punk bands) as shitcore, shitcore as a genre is actually something quite different. It's a pretty self-deprecating and no-fi form of underground music (some of the only real underground music there is currently) that is deliberately awful and humorously pathetic, often created with (or with the help of) shitty computer programs. There are ACTUALLY subgenres within shitcore, ranging from shitgrind to shit rap even, and the lyrics are often obsessed with coprophilia, gay sex, murder, suicide, pedophilia, Hitler, and anything else that can be blatantly offensive, stupid, politically incorrect, or all-around gross.
Examples of shitcore include 50 Ways To Kill Me, Suicidal Rap Orgy, Hitlerbuttsecks, and Kitten Felcher (of which I am a member myself -- good for me, I get an air biscuit).
Naturally, this is what happens when punk rockers get to playing the blues.
Billy Childish, The Jon Spencer Blues Explosion, Boss Hog, the White Stripes, Cash Money, and even some Fear would all be prime examples of punk blues.
While "lo-fi" means music recordings that are recorded raw and dirty (like in someone's basement), "no-fi" refers to recordings that are even dirtier and rawer (usually recorded in places like someone's bedroom with extra noise). Even those who like some "lo-fi" stuff will sometimes run from "no-fi" recordings, especially the extremely noisy, (often deliberately) shitty-sounding ones perpetrated by black metal, shitcore, and noise rock bands.
No-fi: early Gravy Train!!!!
Lo-fi: early Venom
No-fi: some early Darkthrone
Lo-fi: some Cutting Pink With Knives
No-fi: I Killed Techno!
Trashy, seedy, campy rock n' roll with an often androgynous, drunk/drugged out, and b-movie-obsessed disposition. Many trash rock bands are punks reviving the feel of the raunchiest '60s garage bands. Surf rock, rockabilly, and raw garage rock are usually prime components.
The Cramps are Gods of trash rock. They are not its only "big name", but no trash rock fan will deny them and they are probably the biggEST trash rock name.
This term refers to blues music (often very lo-fi at the time) running back as early as the 1930s (probably even before then) that has very sexually explicit and/or suggestive ("blue") lyrics. These are all very old blues songs whose practitioners extolled the use of drugs, the pleasure of sex, etc. Many such songs stand up today as early underground (then illegal) music with explicit lyrics (often, if not always, by black artists, some of whom even leaned toward lesbianism, such as Lucille Bogan).
Lucille Bogan's "Shave 'Em Dry" and Bo Carter's "Banana In Your Fruitbasket" are prime examples of the dirty blues.
Darkpop was primarily an abstractly post-punk type of music that coincided with things like Gothic rock/deathrock and the New Romantics in the late '70s and early '80s (though especially the latter). This means artists inside or outside the mainstream that had dark (yet accessible) sensibilities, but weren't quite Goth or New Romantic (even though there is considerable overlap, admittedly).
Darkpop might include: Fad Gadget, The Smiths, Depeche Mode (mid-'80s to about 1990), some early Ministry. (Note: Ministry originally vacillated between Gothic rock and light, mainstream, New Romantic pop.)
1. Literally ANY music that Tipper Gore and her PMRC cronies were willing to attack.
2. Rock music of any kind that is extremely sexually explicit in nature. Some bands (such as Erocktica and Wank Punter - the latter being made up of people actually involved in the porn business) are deliberately into creating porn rock as a thematical style.
Tipper Gore's porn rock examples range from Prince to the Dead Kennedys to 2 Live Crew to Venom. Self-consciously "porn rock" porn rockers range from pornogrind bands like Cock & Ball Torture to the aforementioned Erocktica and Wank Punter (the latter of whom utilize an apparently comical and diverse delivery a la Spinal Tap). Lords Of Acid and Peaches (despite her post-rock electroclash approach) would probably also be good examples.