An attempt at a collage of online resources for Tolkien collectors:

First the two bibliographies I used to plan my core collection.
Neil Holfords
https://tolkienbooks.net/
should be well known to most senior collectors. The mission statement nothing less than "to list all British editions of the writings of J.R.R. Tolkien (author of The Hobbit and The Lord of the Rings) published between 1910 and 2010, and to illustrate changes to the texts and covers".
Åke Bertenstam's
https://www.forodrim.org/bibliography/tbchron.html
is an excellent overview of where various texts tolkien wrote, translated, edited and commented have been published. I have found this a most excellent resource for finding what publications represent first printings of various material. The last revision of the site was in 2021 so this is quite up to date.

The one thing lacking to a certain extent in these 2 resources are letters. Fortunately we now have
https://www.tolkienguide.com/guide/letters/
For newcomers to the Tolkien Collector's Guide that is just one of many valuable aspects of this site. My personal favorite is the forum where i find various interesting books for sale, check prices, and read up on the minutiae of Tolkien collecting in general. The search function is muchly recommended if you come here seeking information. Chances are good that what you are wondering about is already discussed in the forum. I also find the calendar of upcoming events and publications very useful, https://www.tolkienguide.com/calendar/, and of course there is a store, https://www.tolkienguide.com/store/.

Speaking of minutiae. There is Brian Hendersons excellent
https://silmarillion-minutiae.blogspot.com/
if you consider yourself something of a Silmarillion specialist like myself then this is an amazing resource. Also a good place to learn more about the book as a physical object with regards to binding and quality.

https://hobbithunter.nl/my-collection/
is an excellent resource for hobbit specialists made by Henk Brassien a renowned collector with a collection counting most hobbit editions published. If you wonder about various hobbit editions from around the world this is the place to go.

https://www.tolkientranslations.com/
John E. McLaughlin has made this site an excellent resource for translations/non-UK editions with an extra focus on the Lord of the Rings.

https://tolkienlibrary.com/
excellent site for articles on Tolkien and collecting Tolkien by scholar and collector Pieter Collier. A visit here is an eyeopener for all tolkienites.

https://www.youtube.com/channel/UCnSJnYZv1TQWXuFN0DvSh5Q
Brewing Books. While this isnt the site to see the rare or unusual, I do find this to be just an amazingly inspirational resource. Many short videoes on different Tolkien publications done by a true bibliophile who also knows his Tolkien very well. It doesn't hurt that James voicework is up there with Sean Connery's tour de force 'the name of the rose' :)

https://www.tolkienbooks.us/
This is Devon Press US equivalent to tolkienbooks.net. An excellent resource for US editions. Again a resource i use alot. Point of notice for new collectors is that sometimes the first printings of tolkien material took place in US publications. An example is
'For W.H.A' in Shenandoah.

https://lesarchivesdetolkien.wordpress.com/editions.../
and excellent bibliography of french tolkien editions from Yann Morello.

https://lawrencemvc.wordpress.com/
contains a marvelous bibliography of chinese editions. I recommend this as there have been some sensationally beautiful tolkien publications in chinese the past few years. Sadly Lawrence has left Middle-Earth, but I think his caretakers including our own Zionius keep this site up to date.

http://tolkiencalendars.com/
is The Compleat Gyde to Tolkien Calendars by Phil Goss. If you collect calendars and posters this is THE resource for you.

I also have to mention
https://www.tolkienguide.com/archive/ElrondsLibrary/
This was the archive of Ivan Strelzyks collection with information about tolkien publications in 70 languages from near as many countries. While the old site as such is down it lives on as a part of tolkienguide.com

Thanks to Urulókë for valuable suggestions on resources that had slipped my mind. Feel free to add to this 'bank' of online resources for Tolkien collectors. A big thank you to all the authors behind these resources, many of whom are regulars here at the TCG. You guys are the best.

PS! Åke Bertenstam made an impressive bibliography of books ABOUT tolkien as well. You can find that one here:
https://www.forodrim.org/bibliography/tolklist.html