Coco Blues Company
On the main road at Chaweng Beach, towards the northern end of the beach, near the Iyara Hotel.
This bar / live music venue is quiet during the day and had a good, solid connection. Using your own laptop there beats using an internet cafe - most net cafes in Samui charge 1 baht a minute, so if you are cheap (like me), you can buy a coke for 40 baht and then surf away.
Samui Reef View
Situated between Hin Ta Hin Yai and Hua Thanon.
Free wi-fi access can be found in all areas of the resort and the amenities are open to the public.
Lamai Wanta Hotel
Lamai Beach
This hotel has free open wi-fi. The speed & signal are not bad. The hotel is right in the centre of town (just pass under the big blue "LAMAI BEACH" sign) and is easily accessed from the beach, so lounging by their pool while surfing the net isn't a bad way to pass the time.
Banana Hotel
mid-Chaweng Beach
Free wi-fi is offered.
The Wave Samui
mid-Chaweng Beach
This cool English pub has free wi-fi.
Tropical Murphy's Irish Pub
mid-Chaweng Beach
This cool Irish pub has free wi-fi.
Kitchen Bar
Mae Nam Beach
Newly opened
in December 2010, Greek, Thai Mediterranean restaurant has free wifi.