I'm writing here the contracts that helped me the most and the guides that I'm aware.

nsjames youtube series: https://www.youtube.com/channel/UC_0j3NAYVBiyY152K0f-2og

Kevin Heifner, Webinar from OCI, one of the main EOS committers: https://objectcomputing.com/resources/events/webinars/building-apps-with-eos/webinar-recording - the bonus here is that he teaches you how to **setup the CLion IDE and Unit Tests for contracts**!

RIDL contract: https://github.com/nsjames/RIDL - it's a working one, where you can find the interface right here: http://airdrop.scatter-eos.com/#/

Hack-Til-Dawn EOS Hackathon smart contract: https://github.com/nsjames/Hack-Til-Dawn

Everipedia Whitepaper is perfect to understand a complete well designed dAPP: https://github.com/EveripediaNetwork/Everipedia/blob/master/TechnicalWhitepaper110.md

And of course, the default smart contracts that's inside EOS main repo: https://github.com/EOSIO/eos/tree/master/contracts - try to rewrite the `eosio.token`, then go for `dice` - learned, a lot from them.