The amscd package for commutative diagrams that is included in the / distribution is quite limited. The following packages are worth investigation for authors who need more powerful diagram features: diagram, xypic, pstricks. These are available by anonymous FTP from CTAN (see ctan). The diagram package, by Michael Barr, focuses on commutative diagrams and is thus smaller than the others; it uses / arrows as produced by vector for diagram construction. The xypic package, by Kristoffer Rose, is a more general diagram package; it requires special arrow fonts (included in the xypic distribution) or PostScript capabilities in your system. The pstricks package, by Timothy van Zandt, also provides general diagram object commands; it is strictly for PostScript use, as the name implies.