Note that this is just downtown, if you know of other good cafes with free WiFi (I am particularly interested in Kits, East Van, Gastown and Chinatown) let me know and/or send a report and I'll post it here.
There are plenty of cafes with Fatport i.e. non free WiFi, but I predict that this will fail. WiFi will be free just like water because it's cheaper to make it free than to bill. WiFi users order more coffee and food which is far more profitable for cafes than WiFi. Finally, WiFi is basically free since most restaurants need broadband Internet access anyways for their accounting and credit and debit card validation and WiFi routers and software are only a couple of hundred dollars and getting cheaper daily.
I personally would never have spent nearly the money and time at Take 5 without free WiFi and without free WiFi, I wouldn't have gone more than once to either Tree's or Artigiano (the coffee is good but I am not a coffee geek (yet) enough to go to a place just for the coffee!).
Without further ado, here are the best downtown Vancouver Cafes with free WiFi (in no particular order):
Take 5 Cafe at 429 Granville on the west side just south of Hastings
Caffe Artigiano at 740 West Hastings
Trees Coffee on Granville opposite Take 5