I use bitcoincharts with the function:
That'll cause the newest price to be downloaded, and be refreshed damn fast.
Code:
=Index(ImportHTML("http://bitcoincharts.com/"&"?workaround="&INT(NOW()*1E3)&REPT(GoogleFinance("GOOG");0),"table",4),2,2)
That'll cause the newest price to be downloaded, and be refreshed damn fast.