Great example of an open group desk arrangement. Student desks are in groups, but all face the smart/white/chalk board. This arrangement facilities a great environment for establishing good student-student relationships.
Space Management Room Arrangement Classroom Set Up - Encouraging Collaboration and Self-Directed Learning. This post is full of pictures and ideas. I love how there are so many different places for students to work, and everything is so inviting!
Desk arrangement: put teacher chair in the L of each group for an instant small group, push the four middle ones out for an quick square/round shape. Two desks from each group get folded in and there's an instant group :)