We have Sonos and love it. Currently have it in 5 rooms and will no doubt be adding more in the future.
We also have a Nest thermostat and a couple of the protect alarms. It's great being able to set temp when on the way home etc. It's definitely saved us money on our gas bill. Nest have recently released their outdoor cameras too so may add one of them.
After coming home from holiday to find a hole in the ceiling after the water tank in the loft decided to leak I've been looking at the smart things products and will be getting it soon. Will obviously use the water leak detectors and quite like the idea of the motion sensors to trigger lights. The wireless plugs will be handy too as the gf always worries if she left her straighteners on!