Nekogoroshi-hen - already released as an OVA; less than 60 pages with text; features a picture of Rena, Mion, Satoko, and Rika changing
Kuradashi-hen - "a compilation of the ideas and stories that Ryukishi07 couldn't incorporate into the game"; less than 100 pages with text
Hajisarashi-hen - included with the PS2 game; less than 50 pages with text; looks to be a beach trip (and includes a picture of Takano in a bikini)
Kuradashi-hen looks the most interesting to me, especially because it looks like it includes: