- Solidity Documentation: the official docs
- Web3 Javascript API: web3 javascript api docs
- Solidity Cheat Sheet and Best Practices: quick and dirty cheatsheet
- EthList: The Crowdsourced Ethereum Reading List: other reference materials
- Pet-shop-box: truffle tutorial that teaches you how to build a complete smart contracts application
- Learning Solidity: great youtube playlist with solidity tutorials for beginners