I've been using a Flic (flic.io) button to control the 3 LIFX bulbs in my office, I have one ceiling and 2 uplighter so they're on separate circuits. The flic is stuck on the corner of the regular lightswitch by the door so in general it passes the partner test!

They're not cheap at about £19 plus shipping (although I heard they were available retail in Selfridges), the biggest downside for me is that they're BLE and designed to pair with an iOS or Android device, its not too bad as I have an iPad mini thats permanently sat in the room next door so they use that rather than my phone which leaves the house with me. I saw the other week that they've now released a Linux SDK which allows them to work with the Pi. Some of the reviews aren't great mainly seems to be around the setup and I had problems with mine, I needed a 2nd device to set them up as for some reason they didn't like my iPhone but were fine with the iPad :S Now its all setup though its working pretty well.

In an ideal world I'd have a WiFI version of these but the biggest problem is power, WiFi (well DHCP etc) takes a significant amount of time to connect before it can send its message which means for a lightswitch that you want to respond instantly means keeping it permanently online, this in turn has an impact on battery which means you need it mains powered and that gets bulky and/or awkward to supply.

The amazon dash buttons are a cool concept but they take a few seconds after the push to register the event as they power down, fine for re-ordering toilet roll but not fast enough for lights, in terms of open hardware I've been looking at the ESP8266 modules which are stupidly cheap tiny microcontrollers with built in WiFi, they would seem perfect for things like lightswitches just a case of getting the packaging right.

Also there are much cheaper options on smart bulbs than the LIFX, the Hue White only ones are now sub £15 but you need the HUE hub, the Osram Lightify gets good reports for working with other hubs and its around the £20-£25 mark.