Retweet:

TFSquareOne
TF-1.com's Twitter page, regularly showing article previews and exclusive content before anywhere else

Resource:

20th Century Toy Collector
Mijo's quite spectacular articles on Milton Bradley Transformers, Joustra Diaclones and much more.

TFSource Blog
My weekly articles for TFSource

Joustra-Diaclone.com
Christophe Cassassus's essential Ceji Joustra Diaclone shrine

Heroic Decepticon
Brandon Yap's popular Transformers blog

Robot Points
Ras finally shows off his incredible collection of rarities and unique protos

Mostly Transformers Redux
Eric 'Arkvander' Warren's excellent blog

Mark Of The Takara
Esteban "crazysteve" De Anda's hugely essential copyright and stamping resource for Transformers and Diaclone toys.

TFU.Info
Anthony "Tonyfitz" Brucale's comprehensive Transformers identification and documentation resource.

Paul Vromen - DeviantArt
Paul Vromen's stunning DeviantArt gallery.

Jeroen's TF Page
Jeroen Blok's impressive G1 and pre-TF collection page.

Jon Krause - Illustration
Jon Krause's exceptional illustrations for international media

Retail:

TFSource
Curt Fignar's renowned and ever-expanding Transformers store.