I'm not exactly looking for a new one, my apartment has been pretty great.
I also live way out in the middle of nowhere and there aren't a lot of places to actually rent here.
But, I was thinking of having a look during deskwarming to see if there might be a bigger place nearby to rent.

I heard of the app: Zigbang - but heard it is mostly false listings and false prices on real listings.
I also got told of the website dabangapp - but it seems to be all in Korean, the chrome translate doesn't work, and it shows no available places on it (I know there is 1 place in my town that has been available for a few months, but its 900k won per month (I think, but it is very big and 2 floors - used to be a chinese food restaurant).

Are there any good sites/apps for this?

I second naver 부동산. Zigbang and such apps may work better in big cities, but out in the sticks they are more oldschool. But naver is one site that many realtors use to upload listings. Still, the best would be to hit up some real estate offices because they tend to have some other listings as well, not only the ones you see on the internet.

I don't really understand what StillInKorea means by ''it doesn't deal with villas''. It does deal with everything. Just need to set what you are searching for. Apartments, officetels, villas, detached houses etc and even commercial properties.