Two of the CTAN web servers offer a search facility:
http://www.tex.ac.uk/search and
http://www.ctan.org/search; you can look for a file whose name
you already know
(in pretty much the same way as the
ftp-based quote site index command),
or you can do a keyword-based search of the
catalogue.
The search script produces URLs for files that match your search criteria. The URLs point to the CTAN site or mirror of your choice; when you first use the script, it asks you to choose a site, and stores its details in a cookie on your machine. Choose a site that is close to you, to reduce network load.