There are several options. The smarten IT three toggle that was already mentioned is one of my own favorites, but there are some other choices as well.
Some of the iris devices will also work with smartthings. This includes the button. You don’t need to pay the $10/month fee because that’s a fee you pay to Iris for their rules engine. SmartThings does not have a monthly fee at present except for video storage for cameras. So when you use SmartThings as the controller for the button, there’s no monthly fee.
The following topic (this is a clickable link) lists the various remotes and battery operated wall switches that will work with SmartThings: