This is a post always open to being modified as I find new links to add to it.
I would like to focus on freebies, but some of the material below might come at cost. I will try to note (maybe with a dollar sign, $, which ones are not freebies).
I am maintaining this list for myself, based on products, brushes, plug-ins or stock photos I find attractive, or perceive as being useful, and not necessarily for a broader audience.
✦ ($) Fire Photoshop Action (via Graphic River. Cost: $6.00)
✦ ($) Rusted Sign Mockups (via Media Loot. Cost: $6.00)
✦ 75 High Quality Watercolor Photoshop Brushes (Vol.2) (via Inspiration Hut)