This is an extension of the "Hello World" project for Ethereum and Web3.js which allows you to query the ERC-20 token balance of an Ethereum address.
Try it out here: https://shawntabrizi.com/ERC20-Token-Balance/
http://shawntabrizi.com/ethereum/ethereum-token-contract-abi-web3-erc-20-human-standard-tokens/