WifiAmsterdam
Free
Twenty-nine: Oude Hoogstraat 29
Gary's Muffins: Kinkerstraat 140 (ask for password)
Technically a good list of free WiFi
University
Cafe Crea: ... Grimburgwal-ish
Pay
Cafe Esprit: Spui, facing the square.
Schiphol airport
Hotspot Amsterdam
has paid though extensive coverage in the city center
Friendly
Prins Hendrikkade 100: Prins Hendrikkade 100