I use these sites from time to time (not too often, maybe three or four times a year), but they have been useful in a pinch. If nothing else, they can spark ideas and you can then make your own materials based on that idea.
Busy Teacher – Also free to download materials without an account. Well-organized, huge variety of materials.
iSLCollective – Requires account, but you can log in with your Facebook or Google account to make things quick and easy. Some great stuff on here.
Lanternfish / Boggle’s World – Free, no account needed. Tons of material.
Waygook – Korea-specific forum with tons of lesson plans, materials, activities, and games (of varying quality). Expats in Korea can connect, share ideas, ask questions about Korean culture or life in Korea, etc. Take the extremely negative posters with a couple grains of salt.