Here's an index for names of soldiers who appear in military records, not just rosters.
http://www.itd.nps.gov/cwss/

Records include rosters and a variety of other military docments. There are many types of records, such as hospital, payment, discharge, prisoner of war, death claims and others. If you are stricly interested in rosters, these were taken on a periodic basis, and different names will appear on them, depending on circumstances.

A man named Lorenzo B. Perdue enlisted in Co. "K", 17th Alabama Regiment. Another man named Lorenzo D. Perdue enrolled in Waddell's Alabama Artillery, later Co. "B", 20th Alabama Artillery Battalion. Copies of the service records (including rosters) are available through this website.