This list is fairly accurate in my opinion although I am unfamiliar with some like Mangablobe, Studio Deen, Xebec and... what is the one on the bottom left? It's also missing Artland which I'd place in Mid Tier.
The number of people in this thread who don't know Studio 4℃ or are calling their stuff shit is really ridiculous. Studio 4℃ is one of the studios that are not afraid to step outside of traditional animation and create something new. You don't have to like everything they've done but not to recognize their creativity, talented animators and high production values is just stupid.
If you've never seen Studio 4℃'s stuff watch Memories, Cannon Fodder, Mind Game, Tekkon Kinkreet, Genius Party, Noiseman Sound Insect, Comedy, Koji Morimimoto's Beyond from The Animatrix, Ani-Kuri, Tweeny Witches, Amazing Nuts... all really good stuff.