The subreddit is the heartbeat of the community. It is common for creators to release "community packs" where users vote on themes, and the artist releases the resulting pack for free.
Do not overlook these smaller free packs: dungeondraft asset packs free
While known for paid content, many creators offer "Pay What You Want" (PWYW) packs. You can enter $0 to download them for free, though tossing a dollar or two to independent artists is highly encouraged. The subreddit is the heartbeat of the community