Below is a list of useful links, in no particular order.
Kabcorp DeFRaG movies
QuakeServers.net server list
IGMDB Movie and Demo archive
igmdb.org – Game Movie Database
demos.igmdb.org
ConCarne Download-Area
quakeunity.com
MaverickServers distribution page
router.download.maverickservers.com
ftp.planetquake.com
Mirror by quaddicted.com
Mirror by gamers.org
Mirror by infania.net
Quaddicted files
myT’s files
ftp.idsoftware.com
Mirror by GDWG
Mirror by gamers.org
Q3PLUS File Archive
arrrgh.fr (lots of cool movies)
This site seems to be broken as of 2023-08-17. I’m leaving it here for reference.
media.sourceruns.com (HL1 and 2 speedrun movies)
auri’s q3mme stuff
MediaFire
A copy can also be found in the files.