I also found http://blockcypher.com to be quite nice. In addition to the blockchain API, they also have APIs for creating transactions and even provide web sockets and web hooks. They do not host the wallet so you do not have to share your private key with them. They will create a transaction for you and you can then sign it with your private key. This is a good gateway for developers into the bitcoin system. The alternative is running bitcoind to download the 17 gig blockchain and then start coding. This provides instant gratification for developers to get started.