This where pretty much everyone starts when learning HTML. Even after getting a hang of the basics, I always go back to W3Schools if I forget how to do something or I'm not sure how to write a specific snippet of code. If you want to have a certain thing on your website but don't know how, W3Schools is your go-to.
sadgrl.onlineThis is the quintessential guide to learning coding specifically for Neocities. It goes over the general structure and concepts of HTML and CSS while also having Neocities-specific guides. If you know nothing, start here.
ScriptedWebsite for beautifying websites. It has different snippets of code that you can add to your website to make it look better, as well as scripts to make your website more interactive. Has general how-to guides on a bunch of cool CSS tricks to make your site more visually interesting. If you're looking to make give your site more oomf but don't know what to add, this site has pretty much everything you need.
Last.fm WidgetTutorial on how to make a last.fm widget on your site like the one on my home page. It'll display your last track played, as well as album art and artist.
Collection of random gifs made to look like an online shop. There are so many gifs here there's almost no way you don't find something that you're looking for.
Button WallOver 4,000 88x31 buttons. Has pretty much everything.
The Blinkie HoardA bunch of blinkies.
NukocitiesA bunch of nuko decomail emojis. Some are official emojis while some are custom made by the webmaster. I really like the pride flag ones.
Free TV shows and movies. There might be annoying ads and pop-ups (depending on how good your adblocker is) but it's got an extensive catalog. It's the only site that hasn't gone down, at least not yet.
9AnimeAnime site, with both subbed and dubbed versions of series. The URL changes alot since they get taken down quite frequently, but this link should take you to a page that redirects to the latest URL change.
MangadexRead manga for free. Has different language translations for series. The site is very user-friendly and it's easy to search for new series that you might like by sorting by genre, popularity, etc.
LibgenFree online library. If there's a book you want to read it's here. Sometimes goes down for maintenance but is usually back up within a couple of days.
Z-libraryAnother free online library. You have to join their Discord to ask for book download links so it's less accessible than Libgen. If Libgen is down though I usually go to this one for books.