I want to discover new bands, someone recommended me some metal song? I prefer the nu metal and heavy metal.

Here's some great bands you should definitely listen to:

Maximum the Hormone.
Deicide.
Korpiklaani.
Heidevolk.
Slayer.
Fueled by Fire.
We Butter the Bread with Butter.
HORSE the Band.
Death.
DethKlok.
Children of bodom.
Ensiferum.

I'd like to think I have loads of great bands in my collection, PM me if you want some more.

Are those you posted supposed to be the great ones? :/

I'm just going to say maximum the hormone is the best one of those. The rest of them take themselves too seriously even though they actually can't even write good music. Well, I guess DethKlok doesn't take themselves seriously either but whatever. Death is almost okay, I guess, but there are way better bands who play a similar style.

The thread is way too vague, can you you give us some examples of songs you like or sub-genres more specific than nu metal?

Mushroomhead
Five Finger Death Punch
Soilwork
Trivium

Best I know of...

Alright, since apparently nobody else is going to suggest good bands, I will do that:

Agalloch
Augury
Chimp Spanner
Cynic
Devin Townsend (anything by him)
Exivious
Gojira (the way of all flesh, other albums are mediocre)
Isis
Mirrorthrone
Nevermore (this godless endeavor, other albums are mediocre)
Odious Mortem
Opeth (first two albums?)
Rosetta (first two albums?)
Swallow the sun
Septic Flesh
Sybreed
Textures (drawing circles, other albums are mediocre)
The Faceless
Unexpect

Gojira, yes.
Opeth, yes.

The rest, have no idea... Yet.

Where's Dream Theater?

Clorkwork8: You seriously don't like Slayer? I've nothing more to say to you.

No, they're terrible and I do not give bands credit just for being "influential".

That's just your opinion.
What gives you the right to label a band as 'awful' when millions of others disagree.
I doubt you can even call yourself a metalhead if you don't respect Slayer.
You're just a conformist poser.
I enjoy most, if not all genres of metal, anything from nu-metal to grindcore.
You seem to be trapped in a corner, almost exclusively listening to progressive black metal.
Open your mind, my friend.

Also, getting back on-topic, I'd recommend listening to some Power-Metal to test the water.

Try Blind Guardian or PowerWolf.

1. I do not think it's my opinion, I think they are actually worse than a lot of other metal bands. They just do not write as good of songs. Their drumming and riffs and song structures are usually just boring. It's completely fine if people enjoy listening to their music, and if a lot of people like them. But just because a lot of people disagree with me and think they're amazingly good does not mean there is no truth of the matter, or that I'm wrong. It's a fallacious claim...

2. I do not call myself a "true metalhead". I like many genres of music, not just metal, and I think it would be silly to listen to metal exclusively, or call myself a metalhead. So I don't really think I would count as a "poser" because I am not claiming that I'm some kind of metal arbiter. Also, I don't really get what makes you call me conformist, or what the word is even supposed to mean? If you mean that I choose what music to listen to for how it affects my appearance to others, well... I don't even have any friends who like most of the music I like, and I'm pretty asocial so I don't know why I would want to make others think I'm cool because of my music taste. I just listen to bands that I enjoy listening to. Jeez, you don't have to throw out these personal attacks because I said slayer is bad. Are you sure you are not the person trying to be cool or "conformist" to impress someone else?

3. Only two of the 19 bands I listed are even black metal, and like I said I can enjoy many genres. Metal is only about 1/4 of my music collection, and black metal is like 1/10 of my metal collection... so your comment about that was kind of weird, I think my mind is very open to new music. Having an open mind doesn't mean I have to like some silly thrash bands that are boring to listen to.

4. Wait, are you suggesting to me or the thread starter to listen to some power metal? Well, either way, I like some power metal... Kamelot and Symphony X are good. I do not like the ones you suggested though, sorry.
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Actually I do kind of like some Soilwork, at least A Predator's Portrait.

Dream Theater is sometimes good at songwriting, but the texture isn't really what I like. I like the thicker and colder sounds of Isis and Rosetta.