Before you ask for a TeX macro or LaTeX class or package file to do something, try searching Graham Williams' (Graham.Williams@dit.csiro.au) catalogue, available as help/Catalogue/catalogue.html, or for efficient interactive searching via http://www.tex.ac.uk/tex-archive/help/Catalogue/ctindex.html; this lists many macro packages together with brief descriptive texts.
Having learnt of a file that seems interesting, search a CTAN archive for it (see finding files on CTAN). For packages listed in The LaTeX Companion the file info/companion.ctan may be consulted as an alternative to searching the archive's index. It lists the current location in the archive of such files.
An alternative procedure is to use http://tug2.cs.umb.edu/ctan/, which permits limited `keyword' searching for files on the CTAN sites.