Shvetashvatara

https://www.google.com/search?q=Shvetashvatara

Kaivalya

https://www.google.com/search?q=kaivalya+upanishad

Brihadaranyaka

https://en.wikipedia.org/wiki/Brihadaranyaka_Upanishad

http://www.upanishads.kenjaques.org.uk/

https://www.youtube.com/results?search_query=Brihadaranyaka
https://www.speakingtree.in/blog/maitreyi-and-yajnavalkya-brihadaranyaka-upanishad
https://www.slideshare.net/search/slideshow?searchfrom=header&q=Brihadaranyaka

Link / Text / Book
http://www.swami-krishnananda.org/brhad_00.html

http://vedicheritage.gov.in/aranyakas/brihadaranyaka/

http://nageshsonde.com/images/brihad-aranyak-upanishad-commentary.pdf

Perish

http://345z.blogspot.com/search/label/Perish

Maitri

http://freeglobaluniversity.blogspot.com/search/label/Maitreya
https://www.youtube.com/results?search_query=Maitri+Upanishads

Isha

https://www.google.com/search?q=Isha+Upanishad

gyanopadesam

https://gyanopadesam.wordpress.com/

All become Happy

http://www.allaboutvedanta.com/
http://greenmesg.org/mantras_slokas/vedas-om_sarve_bhavantu_sukhinah.php
https://freeglobaluniversity.blogspot.com/search/label/OMAmenAmeen

Pramana

https://en.wikipedia.org/wiki/Pramana
https://dharmawiki.org/index.php?search=Pramanas
https://www.youtube.com/results?search_query=Pramana
https://www.slideshare.net/search/slideshow?searchfrom=header&q=Pramana

Taittiriya

https://www.google.com/search?q=Taittiriya

https://freeglobaluniversity.blogspot.com/search/label/Brahman

https://freeglobaluniversity.blogspot.com/search/label/RA

Wisdom

https://steadywisdom.com/
http://www.youtube.com/playlist?list=PL6C0500E35A6DF1D2

Academy

https://www.vedantaacademy.in/
http://www.thevedantaacademy.in/

Mandukya

https://www.google.com/search?q=Mandukya
https://en.wikipedia.org/wiki/Soundararajaperumal_temple,_Thadikombu

https://shankarapath.blogspot.com/search/label/Gaudapada
https://freeglobaluniversity.blogspot.com/search/label/Conscious

Main

http://explorevedanta.com/vbc-the-10-main-upanishads/

http://www.realization.org/page/topics/upanishads.htm
http://gita-society.com/scriptures/NINEPRINCIPALUPANISHADS.IGS.pdf

http://en.wikipedia.org/wiki/Mukhya_Upanishads
http://www.indianetzone.com/14/eleven_principal_upanishad.htm
http://hinduism.about.com/od/scripturesepics/a/main_upanishads.htm

http://self.gutenberg.org/articles/eng/mukhya_upanishads
http://vedantaupanishad.blogspot.in/search/label/108