http://amiga.nvg.org/warlock/adf/
Warlock's ADF Archive is one of the first Amiga demo sites I visited. I don't know if it's still updated, but it has a lot of old school and very known demos.

http://cracktros.untergrund.net/news.html
World of Cracktros has a download file which contains 1153 cracktros. The site isn't updated anymore since 2003 though.
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http://www.capped.tv
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www.amigascne.org (Huge archive of Amiga demos, intros, diskmags, packs and so on)

ftp.amigascne.org (The FTP version of the above site)

A.D.A - Amiga Demoscene Archive (Great site featuring a lot of demos with screenshots, comments, downloads and a discussion forum.)

Bitworld (Large database of Amiga demos)
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