I am very sorry for your school's loss. It's never easy, but there are some strategies that may help the kids cope. I've been through three suicides over the years, one in his car in the school parking lot, another a senior who left us on the morning of his graduation. These occurred at two different high schools, and in each case extra guidance counselors came from nearby high schools to help out; some students seemed to feel better talking to someone that they didn't see on a day-to-day basis. It's also important for students to not be allowed to isolate themselves in their grief; having the extra adults on hand allowed us to watch for that.
The most important thing seems to be to talk about the issue but not to allow it to be glamorized. Kids need to grasp that suicide is not an appropriate response to stress. The person who commits suicide is not floating near the ceiling enjoying the sight of others feeling bad and saying "if only...", they are dead. For teachers, that means allowing the facts to be discussed as you feel necessary, but guiding the conversation so it doesn't turn inward and become a round of self-condemnation.
It's also tough to find an appropriate way to memorialize someone who commits suicide, but students often feel the need to do so. Again, you don't want to glamorize the act, but something real needs to be done. If the issue comes up, I would try to guide the kids toward doing something simple - a fundraising drive with the proceeds to be donated to a charity that would have been meaningful to the student who died, or perhaps planting a tree or having a bench with a small memorial plaque put on your school campus somewhere.
As for the possibility of others contemplating suicide, you should never, ever underestimate the power of a simple but heartfelt expression of caring. You don't have to push, you can just say "Hey, are you doing OK? You seem sad lately. If you want to talk, just let me know." This works wonders if you A) really mean it, and B) make an effort to be immediately available to those fragile kids if you sense one of them is reaching out to you.