Multiple Currency Pairs returned in Single API Call
Liqui has an excellent API for currency pairs, and most importantly multiple currency pairs. Documentation can be found here.

Here is an example call that will produce calls for the following currency pairs (using USDt):


BTC -> USD
ETH -> USD
LTC -> USD


Sample output:

{
    "btc_usdt": {
        "high": 4600.0,
        "low": 3956.08280896,
        "avg": 4278.04140448,
        "vol": 712485.2240255205420855,
        "vol_cur": 168.99447489,
        "last": 4379.41785788,
        "buy": 4379.41785787,
        "sell": 4413.6739016,
        "updated": 1504647325
    },
    "eth_usdt": {
        "high": 340.05294292,
        "low": 274.50728822,
        "avg": 307.28011557,
        "vol": 688282.534710083298132,
        "vol_cur": 2250.19082593,
        "last": 318.36785145,
        "buy": 316.78625466,
        "sell": 319.32561326,
        "updated": 1504647325
    },
    "ltc_usdt": {
        "high": 75.0,
        "low": 63.34554099,
        "avg": 69.172770495,
        "vol": 99844.7364654590349569,
        "vol_cur": 1466.92135471,
        "last": 72.00000001,
        "buy": 71.89356482,
        "sell": 72.46986363,
        "updated": 1504647325
    }
}