Organic Aromas is a much loved company around my house. They have the best diffusers that I have yet to use. We especially love that all you put in is the essential oils. This means that the diffused oils are not watered down and no humidity is added to our humid (at times) house.
Even better still is their Signature Blend. Not only does it smell great, but it has helped my wife with some of her (nearly) lifetime long health issues. So much in fact that we had to buy a second diffuser as she didn't want any other essential oils or blends put through our signature blend diffuser.
Dealing with this company has also been a pleasure which makes Organic Aromas a triple threat - awesome products, improves your life and top notch customer service!
As an added bonus, they don't even try to hose you on replacement parts. I actually priced out "building" one of their diffusers from the replacement parts and it barely cost anymore than just buying the diffuser outright. So no big markups on the replacement parts. Especially nice since there are glass components.