Thanks very much everyone. I currently have it working with this in the CMakeLists.txt:
set(MODULE_PYTHON_RESOURCES
Resources/Icons/${MODULE_NAME}.png
Resources/Icons/SSFPIcon.png
)
And this in my module Widget class:
moduleDir = os.path.dirname(slicer.util.modulePath(self.__module__))
SSFPIconPath = os.path.join(moduleDir, 'Resources/Icons', 'SSFPIcon.png')
loadSSFPIcon = qt.QIcon(SSFPIconPath)
self.LoadSSFPButton = qt.QPushButton(" Load SSFP Image Series")
self.LoadSSFPButton.setIcon(loadSSFPIcon)
self.layout.addWidget(self.LoadSSFPButton)