Nagai Tatsuyuki: Director of Toradora, Railgun, Anohana, and Anonatsu. I started Toradora when it was airing, but never finished it. I plan on finishing soon. Anohana, Railgun, and Anonatsu are all wonderful anime. Nagai's anime are always so warm, full of feeling and humor. The characters are always memorable, fully developed, showcasing a wide range of emotion. He is an expert at depicting the bond between friends, and tension. Nagai has an incredible eye, his cinematography, scene composition, and color are always gorgeous. Anohana and (both seasons of) Railgun are two of my favorite anime ever.
Ishihara Tatsuya definitely needs to be mentioned. Chuunibyou, Haruhi Suzumiya series + movie and Nichijou are all awesome works. He was also responsible for the famous Clannad/Clannad: After Story and Kanon, two highly praised shows (which reminds me I should get to watch Clannad at some point). It seems nearly every show he's responsible for is really well-received and I have yet to see him fail. I'm just going to ignore Endless 8
My only complaint about Ishihara is that most of his anime follow a formula. It is a good formula, and he makes great anime, but it's still a formula. Apathetic guy meets quirky, energetic, socially isolated girl, they accidentally become friends, madness ensues. That is really just nitpicking on my part, it does not really take away from his greatness. When all is said and done, Miyazaki movies follow an even more rigid formula, so I can hardly fault Ishihara. He's definitely one of my favorites. I started watching anime again specifically because of Chuunibyou. I was not missing a new series by the director of Haruhi and Clannad. I have not seen Nichijou yet, but plan too eventually.