user28219: I would like to check quotes from multiple bitcoin exchanges in a single, aggregated place. Is there such a service or at least something in that direction out there? Or do I have to connect to each and every exchange and get their market data by myself?

user30041: Coral Blocks has a free service that provides aggregated liquidity from Coinbase, Coinsetter, Okcoin and LakeBTC. You can get the aggregated book in JSON through the link:
http://www.coralblocks.com:45453/book/BTC-USD
{
    "last updated":     "20151015-21:01:27.551",
    "time zone":        "America/New_York",
    "symbol":           "BTC-USD",
    "exchange":         null,
    "spread":           -0.90,
    "best bid size":        0.07000000,
    "best bid price":       255.87,
    "best ask size":        0.00090000,
    "best ask price":       254.97,

    "bids": [

        [ "OKCN",       0.07000000,     255.87],
        [ "OKCN",       0.07000000,     255.84],
        [ "OKCN",       0.07000000,     255.81],
        ...
    ],

    "asks": [

        [ "LAKE",       0.00090000,     254.97],
        [ "LAKE",       0.06700000,     254.98],
        [ "LAKE",       0.60000000,     254.99],
        ...
    ]
}

You can also get real-time updates through TCP and FIX. More info about the API here: 
http://www.coralblocks.com/index.php/2015/10/free-real-time-bitcoin-market-data/
Disclaimer: I am a developer at Coral Blocks.

28219: <p>I would like to check quotes from multiple bitcoin exchanges in a single, aggregated place. Is there such a service or at least something in that direction out there? Or do I have to connect to each and every exchange and get their market data by myself?</p>
 30041: <p><a href="http://www.coralblocks.com" rel="nofollow">Coral Blocks</a> has a free service that provides aggregated liquidity from Coinbase, Coinsetter, Okcoin and LakeBTC. You can get the aggregated book in JSON through the link:</p>

<p><a href="http://www.coralblocks.com:45453/book/BTC-USD" rel="nofollow">http://www.coralblocks.com:45453/book/BTC-USD</a></p>

<pre><code>{
    "last updated":     "20151015-21:01:27.551",
    "time zone":        "America/New_York",
    "symbol":           "BTC-USD",
    "exchange":         null,
    "spread":           -0.90,
    "best bid size":        0.07000000,
    "best bid price":       255.87,
    "best ask size":        0.00090000,
    "best ask price":       254.97,

    "bids": [

        [ "OKCN",       0.07000000,     255.87],
        [ "OKCN",       0.07000000,     255.84],
        [ "OKCN",       0.07000000,     255.81],
        ...
    ],

    "asks": [

        [ "LAKE",       0.00090000,     254.97],
        [ "LAKE",       0.06700000,     254.98],
        [ "LAKE",       0.60000000,     254.99],
        ...
    ]
}
</code></pre>

<p>You can also get real-time updates through TCP and FIX. More info about the API here: </p>

<p><a href="http://www.coralblocks.com/index.php/2015/10/free-real-time-bitcoin-market-data/" rel="nofollow">http://www.coralblocks.com/index.php/2015/10/free-real-time-bitcoin-market-data/</a></p>

<p><strong>Disclaimer:</strong> I am a developer at Coral Blocks.</p>
