You need a hub to orchestrate all of your z-wave or zigbee devices (light switches, etc.) None of the hubs are prefect, but this one is easy to set up and relatively stable. The built in automation software, however, is abysmal. That is why we recommend (below) using third party products. The only way to get better than this is to set up your own hub using a Raspberry Pi, but that is not approachable to the average consumer.
This workflow building software will have you coordinating events in your house in no time. It's visual, easy to use, and free! What can be better than that. It works on iOS and Android.
To control conventional lighting for on/off, this is the switch to get. The toggle shape works intuitively like a conventional switch, so there is literally no learning curve. This connects easily to your SmartThings hub.
And you can make it a 3-way with this add on.
Just like it's cousin above, this switch works the same way but allows dimming of conventional bulbs. Tap up or down for on or off. Hold up or down to change the brightness.
​And you can make it a 3-way with this add on.
The two top contenders in this space are the Philips Hue and this bulb. This one is brighter, has a richer color range, and doesn't require a hub, unlike it's competitor. It also seems to have a stronger range of capabilities, such as fade on from 0 to 50% over 30 minutes.
This is the lease expensive and very mature solution to adding voice control to your home devices. It's been around the longest so integrates with almost anything you might want to buy. It's new intercom feature makes adding this throughout the house a compelling option.
If you want a fully featured voice search, Google Home is going to be a better product, but it's significantly more expensive, especially if you want to put then in every room.