If access to an institutional ECN aggregator was readily available (unfortunately, it's not) the best solution for a "tape" would be streaming the best bid via API.Quote from Worldcrusher:
In the equities market, I can watch the tape to get a sense of what is going on before I enter a trade. In Forex, is there an equivalent?
http://vcapfx.com/cax-portal-aggregator.asp
http://flextrade.com/flexfx.php
You could do the same with IB's API (see attachment), but the price changes wouldn't be as indicative of the overall market as the aggregators.