I just discovered the handy apt-file command in Ubuntu today while trying to resolve the dependencies need to install Hpricot. With this utility, you call search through all the packages in your repositories (installed and not installed) for a given file. For example:

apt-file search stdlib.h

Will return a list of packages with that header file. In order for this command to work though, you’ll need to at least have ran this command once:

sudo apt-file update