Besides office work or filing documents at the court house what other kind of volunteer work at a law firm can a law student do?

At a law firm, you'll probably end up doing "office work" of the paralegal or legal secretary variety. Malpractice insurance restrictions usually eliminate anything more exciting. However, many county court systems now use volunteer mediators. You get trained through the county, and can mediate in small claims court, family court, divorce cases, landlord-tenant cases, and sometimes even traffic court. You'll get a fascinating insight into the REAL concerns of the ordinary people involved, concerns that go far beyond the law. You'll write resolution contracts for the parties involved in the action. And, you'll be working as a partner with the judge in charge of the case. To find a volunteer mediation group in your area, check the phone book under "mediation", or ask a judge, or try the county social services people.

Addition: "At a law firm, you'll probably end up doing "office work" of the paralegal or legal secretary variety. Malpractice insurance restrictions usually eliminate anything more exciting."

That's not necessarily true. Depending on the size and type of Law firm you work for, you will probably be doing legal research for attorneys. This entails looking up cases, determining substantive legal issues, and providing the information to attorneys. This can be very interesting, and is not just copying and/or legal secretarial work.

People without a law degree can do nearly everything that a lawyer does except "practice law" (which generally includes establishing relationships with clients, setting legal fees, giving legal advice, or representing a client before a court or on the record). Aside from these four things, a wide variety of legal work exists that is both interesting and substantive (i.e., not filing papers or organizing redwelds).

In addition to research, you would also probably do the type of work that paralegals do, such as organizing case materials, summarizing/drafting pleadings and other court filings, and reviewing documents. I would suggest looking for a medium or larger sized firm in a large city (Like Washington DC, Chicago, or New York) if you want more substantive legal opportunities as a clerk.