Useful sites
>Otaku-centered art
https://www.pixiv.net/ - (need an acount to browse)
https://yande.re/post - High resolution anime art including pools for artbooks
http://tsundora.com - Similar to yande.re and has high resolution anime art.
http://konachan.com/ - Anime wallpaper booru.
>Finding the source of an image
https://saucenao.com/ [good for manga]
https://iqdb.org/ [good for works found on booru/pixiv]
https://ascii2d.net [good for works found on twitter/pixiv]
https://trace.moe/ [good for screenshots from anime]
>if it's cropped these are the only ones that will work
>Torrenting
https://nyaa.si/ - for SFW torrents.
https://sukebei.nyaa.si/ - for NSFW torrents.
https://nyaa.pantsu.cat/ - less active alternative.
https://coalgirls.wakku.to/torrent-listing
https://animetosho.org - Anime DDL+NZB mirror
>Hentai
https://hitomi.la/ - Doujinshi and hentai.
https://hentaihaven.org/ - animated