How can I create a sense of community in a research group?
Enthusiasm: Students in a lab should get the feeling that the professor is someone who shows as much interest and puts in as much hard work in the project as themselves. The professor may have a lot of credentials and experience, but his enthusiasm level must be the same as that of his students.
Emotional management: Sometime there could be students who lose their focus on research; at others, there could be slight rifts and differences in opinion between the professor and student because of their approach to the problem. There may also be problems within the students which could be distasteful. The professor must be mindful of these, try his best to ameliorate the situation and not let things go out of hand. Without getting smarmily personal, the professor must manage his lab as though it were his second family.
Ensuring good placement: Placement is not an indicator of research, but in reality, people use this record to gauge a lab's quality. The professor must build contacts and be willing to counsel and recommend their students to good places (each according to his ability, etc).
Good Results: The most important point. If students must feel a "sense of achievement from simply being part of the lab", then the output from the lab should be sensational. This involves a lot of man-management; knowing what each student is good at and how to get the best out of each one of them. Finally, though it may sound cliched, hard work is the key to good results.