You don't say where your passports are from, but if you're in Europe, there's London.

There are many startup and entrepreneur events on meetup.com, such as minibar, london bloggers.

Also, in terms of a geographical 'valley', there's Silicon Roundabout ( http://www.google.com/search?hl=en&q=silicon+roundabout&... )

Ah, relatively low costs - that could be the kicker. London is an expensive place to live. That said, one can still live frugally by cooking for yourself rather than eating out, and the GBP has fallen in value so it's become a cheaper place for those dropping foreign currency.

Finally, GOOD LUCK in your venture - keep us posted on your unnamed product, and where you're heading, in whatever sense of the word :)