We have started the project during a hackaton here at Themeisle and just managed to launch a beta version for it.
While before I was wondering why there aren't any good tools for this, soon I realise that is much more complex than I thought, for now we are using various existing APIs from Godaddy,DomainsBot and DataMuse with custom rules, exclusions and suggestions to make sure we deliver much better results.
It seems that the only good solution for now and something we are working on is to integrate MTurk or microworkers and generate suggestions "on-the-fly", while building a nice database of data, I am passionated about ways that we can build a smart searh/suggestion engine "backed" by humans, will see how much it makes sense.