The intro to 'Ov Fire and the Void' by Behemoth.
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There's tons of it in some metal genres, but it might not be your thing so it would help to know what sort of music you'd like to play. For more mainstream music, for example "Knights of Cydonia" by Muse has some pretty easy tremolo picking and it's a fun song.
Go check out some black metal, that will build your picking strength fast, something really easy but good for tremolo picking is I Am The Black Wizards de Emperor.
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Misirilou is were trem picking began, but there's...
[forbidden link] <<< Morbid Angel - Summoning Redemption. One there more listener friendly songs. They trem pick chords a lot.
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Just about any black metal. Or any Dick Dale, if you'd prefer something that other people will want to listen to.
Dream House by Deafheaven and It Took The Night to Believe by Sunn 0))) are great ones for excercising. Less tedious ones where you use the skill in conjunction would others would be stuff like Filial by Pianos Become the Teeth and A Glass Can Only Spill What It Contains by mewithoutYou.
If you're a metal player Holy Wars from Megadeth is a great and accessible tune - it's not constant tremolo picking, but rather bursts of it - which makes it more accessible.

Slayer - War Ensemble.

Surf Guitar - Dick Dale would be the obvious choice here.

Intro to "wasted Years" Iron Maiden and the main riff Back in the Village Maiden - these would be pretty easy.

Every indie band from the last 10 years - they love those reverb drenched tremolo picking leads!