If you are looking for API for cryptocurrencies, below are the list
1 Coinmarketcap
is one the best APIs providing website
They provide JSON,RAW FORMAT,CSV FORMAT etc..
eg.
https://api.coinmarketcap.com/v1/ticker/
get the first 10 coins - https://api.coinmarketcap.com/v1/ticker/?limit=10
Get the first 10 coins and convert to EUR , https://api.coinmarketcap.com/v1/ticker/?convert=EUR&limit=10
They provide widgets that you can plug in in your blog or website https://coinmarketcap.com/widget/
2 Coingecko
If you want to download the bitcoin price for last 90 days in csv or excel format you can download from https://www.coingecko.com/en/price_charts/bitcoin/usd
This site provide bit coin price minute wise. You can download charts and graph on crypto currency price changes for last 90 or MAX days.