Anyone staying at the Mövenpick near Centraal station? That's where I ended up getting accommodation at...believe it or not, was able to get a room there for just 15e more a night than it would have cost at Hotel Ibis near Centraal station!

I had corresponded with some of my Dutch friends who said that Hotel Ibis Amsterdam City West is nearest to the Summit, but in terms of transportation (not having to change buses) Hotel Ibis near Centraal station would be your best bet.