There are many companies invested in the Matter smart home ecosystem, but not all of them are fully committed. Some see compatibility as central to their visions of the future, while others do little more than the bare minimum. If you want to build your smart home using products from companies that are all-in, this list is a good place to start.
1. Samsung
Samsung makes more household appliances and consumer electronics than just about anyone (if not everyone). It sees Matter as a key component in enabling Samsung alliances and devices to be central components in our internet-connected and remotely-controllable homes.
Samsung SmartThings was one of the first smart home ecosystems to embrace Matter, and it continues to adopt new versions like Matter 1.4 faster than most of the competition. That's not to say all is perfect. Various Samsung appliances like TVs and fridges may serve as Matter hubs, but they're not Matter devices themselves that you can control from outside the SmartThings app.
2. Aqara
Aqara is a younger company that, from is inception in 2009, has exclusively focused on the smart home. It sees Matter as central to its stated mission of "making smart home experiences that are accessible to everyone."
Like Samsung, Aqara's hubs also support the latest version of Matter, enabling you to control the widest range of devices and take advantage of the newest features. Aqara produces a wide-range of smart sensors, lights, switches, door locks, and other smaller but vital components of an interconnected home.

Aqara Hub M3
The Aqara Hub M3 is a Matter-compatible gateway that connects and manages up to 128 smart devices, facilitating local device automation without relying on Wi-Fi.
3. Tapo TP-Link
TP-Link is well known for its internet routers, but the company has a large smart home line by the name of Tapo (replacing is previous "Kasa" line, which you may still see for sale). Tapo's Matter-compatible offerings are often among the cheapest in their categories, like light bulbs and power outlets.

Tapo Smart Plug, Energy Monitoring
A compact Matter-certified smart plug offering cross-platform control and energy monitoring through the Tapo app.
More recently, Tapo has also turned Deco mesh routers into Matter hubs. This is an ideal solution, since mesh routers are naturally spread throughout the home, reducing the likelihood of issues stemming from gadgets being too far from your hub.
4. Govee
Govee is a significantly smaller company, one primarily (but not exclusively) focused on specialized lighting. The company provides you with an abundant selection of Matter-compatible bulbs and light strips, but that's just the beginning. Govee also offers backlighting for your TV, innovative floor lamps, and curtains made of lights.

Govee Neon Rope Light 2
Version 2 brings upgraded clips, more flexible installation, Matter support, and automatic shape recognition using the app.
Advanced features still require the Govee app, but you can handle the essentials over Matter, like changing colors and seeing up basic automations.
5. Switchbot
Surprisingly, there are still device types we have yet to cover. If you want smart shades for your windows or smart shower curtains, all controlled via Matter, where do you turn? Switchbot has you covered. This is also one of the first companies to offer a Matter-enabled air purifier (just don't expect many of the features to be available through Matter just yet).

SwitchBot 4 in 1 Air Purifiers Table
A compact, multi-functional table that combines air purification, wireless charging, ambient lighting, and more, tailored for pet owners and smart home enthusiasts.
Switchbot's multifunctional, modular robot vacuum supports Matter as well. Even those Switchbot products that lack built-in compatibility can be made compatible by buying a Matter bridge.
6. IKEA
IKEA's bread and butter is selling you everything you need to furnish a home. Surprisingly, that includes a long list of IKEA Matter devices. IKEA offers a Matter hub along with options spanning smart buttons and sensors to smart lighting and an air purifier. It's the largest big box retailer to offer its own store-brand Matter products.
These Three Brands Still Have Major Work to Do
You may have opted to build your smart home with Amazon Alexa, Apple Home, or Google Home at the center. Unfortunately, all three of these platforms have lagged when it comes to Matter support. At the time of writing, Google Home can't control a Matter air purifier or vacuum, since the platform remains a few versions of Matter behind.
Between the six brands listed above, you have basically everything you need to make an all-Matter smart home. You're welcome to explore other offerings, but at least you know you'll know you're starting with a solid foundation.