I'm definitely going to 'third' that recommendation of Refused. Motherfucker I love that band! The Shape Of Punk To Come, Poetry Written In Gasoline, New Noise, a bunch of others. What an awesome band.
You might like International NOISE Conspiracy. Download the track "Timebomb" by them.
I'm going to agree with Storm Rider, even though I never caught on with Nevermore much, but the rest, definitely.
The newest Trivium album, "The Crusade" sounds exactly like old school Metallica with more pop hooks and singsonginess. They shred almost too much, sometimes. You would definitely be down with that.
Also, get Nonpoint's "Development" album. Very catchy, very well written, very accessible, and yet, on the harder edge of nu-metal.
Now here are my most enthusiastic recommendations:
Opeth - the songs are even longer than the Metallica you've been listening to, but you should be able to dig it, if you give it a chance. Mandatory tracks: The Drapery Falls, The Moor, White Cluster (I could go on but that's already like half an hour)
Porcupine Tree - The guy that produces Opeth, Steve Wilson, plays guitar and sings in, as well as produces this band. Amazing material, ranging from heavy to soft, always cool and accessible, yet mature and complex. Fucking great band. Just get everything by them. But if you want a sample first, listen to "Wedding Nails" "Collapse The Light Into The Earth" and "The Sound Of Muzak"
Tool - My favorite band... you must know of them. System Of A Down are among my favorites, and I find most SOAD listeners love Tool as well. If you haven't listened very extensively, check out these tracks. "Jerk-Off," "Sober," "Bottom," "Forty-Six & 2," "Eulogy," "The Grudge," "Ticks and Leeches," "Jambi," and, finally "Right In Two."