From 2008 to 2013 today, the following companies either proved their worth in the marketplace by winning top honors or simply piqued my interest because they looked good. Since the games are all covered thoroughly at Omochikaeri, there's no point discussing the games in particular.
What's more interesting is how many new companies have established their worth than were around in the past. Frontwing, August, Feng, Navel, Minori, Key, Type/Moon, and Windmill we could expect would make more good games. But who saw all these new companies suddenly taking the lead?
Alcot, Lillian, Lump of Sugar, Palette, Sphere, Yuzusoft, Ryokucha, Saga Planets, Nitroplus, Caricature, Sprite, Clochette, Favorite, Asa Project, and Pulltop all climbed to the top of the sales rankings from out of nowhere against established giants like Circus and Key. Now it's just unknown who is the best visual novel company anymore. Everyone has their fans and the consumers are split between many more competing interests than ever before. Let's hope the competition encourages improvement instead of just a series of bankruptcies.
As for the still unnamed companies, I just found their games interesting or uniquely attractive. The general public doesn't really agree with my remaining choices. Rosebleu, Debu no Su, Journey, Moonstone Cherry, Wheel, Sorahane, Onomatope, and Tone Works just put out what to me look like really good looking games.
Of these mentioned titles, Grisaia is getting an anime, Fortune Arterial already has one, Daitoshokan no Hitsujikai is getting one, Tayutama has one, Mashiroiro has one, Shukufuku no Campanella has one, Oretachi wa Tsubasa ga Nai has one, Yosuga no Sora has one, Steins;Gate has one, Hoshizora e Kakaru Hashi has one, and Koi to Senkyou to Chocolate has one. The rest have been left to the winds of fate.
Furthermore, a lot of games aren't mentioned on this list, for instance Da Capo III. This is because any game that's a sequel or spinoff of an already mentioned game in this list or the previous list isn't necessary to include. Every game I include means I'm including the entire franchise, and consider the whole franchise worth reading/playing/watching. Almost all of these games have at least one sequel, which means this list is actually larger than it seems. If you played all of these games and everything related to their franchises, I suspect it would take years. This is, after all, the entire accumulated art of every last good visual novel ever made by every last good company. It should last a while.
Alcot - Engage Links, Osananajimi wa Daitouryou, Real Imouto ga Iru Ooizumi-kun no Baai
Lillian - Twinkle Crusaders
Frontwing - Grisaia
August - Fortune Arterial, Aiyoku no Eustia, Daitoshokan no Hitsujikai
Lump of Sugar - Tayutama, Hello, Good-bye, Hanairo Heptagram
Palette - Mashiroiro Symphony
Windmill - Shukufuku no Campanella, Witch's Garden
Navel - Oretachi wa Tsubasa ga Nai
Sphere - Yosuga no Sora
Yuzusoft - Tenshin Ranman Lucky or Unlucky?, Dracu-riot
Ryokucha - Koiiro Sora Moyou
Saga Planets - Kisaragi Gold Star, Hatsuyuki Sakura
Nitroplus - Steins;Gate
Rosebleu - Tiny Dungeon
Caricature - Bitter Smile
Feng - Hoshizora e Kakaru Hashi
Debo no Su Seisakusho - Sora o Aogite Kumo Takaku, Toki o Kanaderu Waltz, Hanasaku Otome to Koi no Grimoire, Hanachiru Miyako to Ryuu no Miko
Sprite - Koi to Senkyou to Chocolate
Journey - Nanairo Kouro
Moonstone Cherry - Imouto Paradise
Clochette - Kamikaze Explorer
key - Rewrite
Asa Project - Renai O km
Wheel - Bura Bura
Favorite - Irotoridori no Sekai
Minori - Natsuzora no Perseus
Sorahane - Sakura, Sakimashita
Onomatope - Sakura no Reply
Pulltop - Kono Oozora ni, Tsubasa o Hirogete
tone works - Hatsukoi 1/1
type/moon - Mahoutsukai no Yoru - Witch on the Holy Night