Multi color LED smart light bulbs. I had done a few LEDs years ago for frequently used lights, but I'm glad I didn't go overboard back then because it'd be harder to justify swapping out LED bulbs. Being able to set and change colors is really enjoyable. Dimming is very convenient too, though they don't get to the "barely on" dimness that I could get with incandescent bulbs on a slide dimmer. I can use timers, group lights together, or split lights that are on the same switch. It's very handy to change a light to bright white for hobby projects or winter grilling on the back deck. I guess I can also sync lights with music, though I haven't played with that.
The only thing I might have done differently is to get bulbs controlled by a hub, to reduce the number of devices on my wifi. It's quicker, cheaper and easier to do a few by wifi, but I don't think it's so good to have a bunch of smart devices sharing my wifi.