If you like, you may use one of these bibtex entries for Macaulay 2. The first version is for use with the hyperref macro package.
@Misc{M2,
author = {Grayson, Daniel R. and Stillman, Michael E.},
title = {Macaulay 2, a software system for research
in algebraic geometry},
howpublished = {Available at
\href{http://www.math.uiuc.edu/Macaulay2/}%
{http://www.math.uiuc.edu/Macaulay2/}}
}
@Misc{M2,
author = {Grayson, Daniel R. and Stillman, Michael E.},
title = {Macaulay 2, a software system for research
in algebraic geometry},
howpublished = {Available at http://www.math.uiuc.edu/Macaulay2/}
}