The Etherscan Ethereum Developer APIs supports both GET/POST requests and a rate limit of 5 requests/sec.
To use the API service please create a FREE Api-Key Token from within the ClientPortal->MyApiKey area which you can then use with all your api requests.
You may receive a HTTP 403 error if exceed this limit.
Kindly credit/link back or mention that your app is "Powered by Etherscan.io APIs" would be very much appreciated.
Note: The Ethereum Developer APIs are provided as a community service and without warranty, so please just use what you need and no more.