There's also http://www.forex.com/forex-api.html , but the list of bad reviews of forex.com/GAIN capital is quite large, the question is if you want to associate yourself with them.
http://www.lmaxtrader.co.uk/apply-for-an-account
"Please note we are unable to accept applications from US residents."
That's a shame...
Another option is Dukascopy, with a $1000 minimum opening balance. However, their API is a Java one...
I suggest http://www.lmaxtrader.co.uk/ (relatively well-regulated real marketplace with sometimes low spreads, low startup costs and a free API with TCP/IP interface) and http://esper.codehaus.org (NEsper if you don't want to use Java). This should be enough to cover all needs.
I find it incredible that only OpenTick used to have a somewhat usable service. CQG, for example, has a seemingly good service, but their time stamps have a minute granularity!