Any Vision – A Lightroom plugin that uses Google Cloud Vision to analyze your images and suggest keywords for it.
Wordroom – Another Lightroom plugin that suggests keywords for the images in your catalog
Photerloo Instagram Hashtag & Keyword Generator – A web site that lets you upload a photo and then suggests keywords or hashtags for it. Works surprisingly well. While not strictly Lightroom related, it’s a good way to get the ideas going.
List of Lightroom presets by Photolemur. Paid and free.
TK Actions v5 resources – Tony Kuypers launch page for information on using his TK Actions Photoshop panels for creating luminosity masks