This site provides you with information about all the packages available in the Debian Package archive.
Please contact Frank Lichtenheld if you encounter any problems!
There are shortcuts for some searches available:
http://archive.debian.net/namefor the search on package names.
http://archive.debian.net/src:namefor the search on source package names.
This search engine allows you to search the contents of Debian distributions for any files (or just parts of file names) that are part of packages. You can also get a full list of files in a given package.