Also known for incorporating real-life landmarks in their series' backgrounds. For instance, Haruhi is set in and around Nishinomiya, a small town near Kobe. Lucky Star is set in Saitama Prefecture, north of Tokyo (the Hiiragis' shrine is based on the actual Washinomiya Shrine and Konata's house is based on creator Kagami Yoshimizu's house in the town of Satte, all have developed The Red Stapler-type followings by otaku). The school in K-On is located in Toyosato in the Shiga Prefecture near Kyoto, while most other locations are set in Kyoto itself.
The studio also has a thing for colorful eyes for their characters, and uses this to great effect when the cast of the show they're animating have otherwise "normal" hair colors (stylized blacks or browns). Seen to full effect in Hyouka, where Chitanda's purple eyes were often used to underscore a point.
And one more thing they're really famous for: from K-On onward, their ED animations tend to be done in a MTV-style fashion, usually featuring the lead females (or males in the case of Free!) performing the ED song in a context wildly different from the actual content of the show.