Live instances

Public

These are public sites running GNU MediaGoblin:

http://roaming-initiative.com/mediagoblin/ running on http://hyperboria.net/ apparently! reddit thread
https://goblinrefuge.com -- Registration open. Images and video enabled.
https://papers.goblinrefuge.com/ -- Registration open. Document uploads enabled. Targeted toward papers and presentations.

https://mediagoblin.pixelminers.net/ -- Registration disabled. Fast, secure (HTTPS enforced) Mediagoblin server. Supports Pictures, Music and Videos. Alternatively it is also available as a Tor hidden service/Onion Service.
http://barn.kerosenecow.net/ -- Registration disabled. This is mainly a showcase for development of the MG-GIMP project (a Mediagoblin plug-in that permits hosting of GIMP images and resources).
http://isengaara.de (not running as of 13 Oct 2014) -- IsengaaraP's mediahub for sharing eCantorix songs and コスプレ photos.

https://efjz.in -- "EricFontaineJazZmediagoblIN" is for me to archive recordings of music performances of me and my fellow musicians. [25/01/2016 : it is a ownCloud instance]
http://mediagoblin.com ("502 Bad Gateway" as of 11 Jan 2016; hosted media are accessible) -- Currently registration and video are disabled; you have to ping Chris Webber for an invite.
https://gobblin.se (previously mg.wandborg.se) -- Registration open, but uploads are currently broken (help fixing is welcome!); all media types enabled (except STL/3D, at the moment) -- details; Joar/mg.wandborg.se.
Your browser may not trust the certificate authority: http://wiki.cacert.org/InclusionStatus.
https://mediafrom.me - Registration by request, but new requests are welcome!! Contact j1mc on IRC / Jim Campbell (jcampbell - ate - gnome - dot - org) for an account. Supports pictures, raw images, video, & partly supports 3d printing schemas (fancy, live Blender rending doesn't work with Rackspace Cloud files).
https://media.kotori.me/ -- Registration open. Images, video, audio, raw images, ascii art, stl models, and pdf enabled.

These are instances run by organizations, usually having registration limited to organization members:

http://medii.ceata.org -- Fundația Ceata, Romanian Free Software and Free Culture activist organization. Registration is currently disabled.

http://media.libreplanet.org -- Videos of the LibrePlanet 2013 conference (Free Software Foundation). Registration is currently disabled.

https://mediagoblin.chicagolug.org -- Slides and photos from events and meetings of the Chicago GNU/Linux User Group. Registration is currently disabled.

http://media.bibliolabs.cc -- Repository for handling media at Sistema de Bibliotecas Públicas de Medellín (SBPM), installed as part of the biibliolabs project which aimed at exploring open source software and open licenses for knowledge management for public libraries in Medellín, Colombia, South America

http://mediagoblin.tami.org.il -- Media repository (documents, videos, images) for Tel Aviv Makers (telavivmakers.org / tami.org.il), a hackerspace in Tel Aviv, Israel. Lots of random stuff.

http://midiacapoeira.in/midia -- Material from Mídia Capoeira, a brazilian independent journalism initiative which promotes tactical-radical mediactivism. Registrations are open to facilitate non-identifiable uploads and leaked material. (down since august 15. Down notice - in portuguese)

Also, these sites are running MediaGoblin, but are for more limited audiences (family/friends of person who's running it, etc):

haise family photos (currently with a baby focus)
jpope's instance -- Registration currently disabled.
thelovebug's instance (registration closed)
mediagoblin.aurka.com janssen’s personal mediagoblin-instance with concerts, demonstrations and other stuff (registration closed)
media.chrishancockart.com Artwork from Chris Hancock. (registration closed)
photos.technicallyandrew.com Photos by Andrew Browning (registration closed)
media.larjona.net Laura Arjona's pictures and videos, family, and libre software stuff (registration closed)
media.mnalis.com family photos and cycling events for biciklijade.com (registration closed)
Barry's instance Mostly videos and photos of the family.
media.strugee.net, which is run by Alex Jordan and mostly used for personal photographs (registration closed)
media.micha.elmueller.net Photos by Michael Müller, all licensed under CC-BY (registration closed)
James' instance James' family media sharing site (registration closed)

maiki’s baby photo site (can't connect on 20 Dec 2015)
spaetz' private pics (502 Bad Gateway on 20 Dec 2015) Sebastian Spaeth's pictures, family and stuff (registration closed)
gallery.Dick-Thomas.co.uk (Server not found on 20 Dec 2015) Dick Thomas' pictures, family and stuff (registration closed)
media.wigunnara.com (Server not found on 20 Dec 2015) Giri Alam's pictures, family and stuff (registration closed)
noreal.info/galeria (does not open on 31 Dec 2015) Run in a Raspberry-pi by Arder Vegan (registration closed)
ardervegan.info/media (Server not found on 20 Dec 2015) Run in a Raspberry-pi by Arder Vegan (registration closed)
[1] (can't connect on 31 Dec 2015) Pictures and music from Charles Pehlivanian, hosted on a Raspberry Pi.
photos.katsarov.org (no GMG on 20 Dec 2015) Photos by Anton Katsarov (registration closed)
media.deadsuperhero.com (Server not found on 20 Dec 2015) Artwork and photos from Sean Tilley, who writes MediaGoblin themes for fun.

You can add your instance here, too!