Many folks have hacked the Amazon Dash Buttons into internet of things workhorses, apparently so many that Amazon has made it available as a device to buy on it’s own for $20! You can configure this button for 3 actions, short click, long click, and double click. It works on WiFi so no fancy extra protocol or receiver to worry about. You can order them now for mid may 2016 delivery (UPDATE: Now just register to be emailed when they are available)
It does seem that it only works with AWS services. It would be nicer if you could configure it to just post to website or something similar. I’ll be picking one up and will update you when it’s in!