While I don't host any of my own backgrounds here, resources are linked below for seamless / tiling BGs.
★ = Personal favorite

• Vinizinho.net
• Nonexistent Fandoms Fandom
• Betty's Graphics
• Rivendell
• Rachychel ★
• Pixel Moondust ★
• Pix.crd.co
• Texture Town
• sadgrl ★
• Freebackgrounds
• hekate