xmltv
XMLTV is a set of Perl scripts which grab the TV listings from various sources and provide a standard XML output.
It can be used to provide the TV listings to TVHeadend for example, but you can use it separately too (from the command line).
After installing, run your favorite grabber with the "--configure" parameter; then you can use it on the command line or in TVHeadend by selecting it from the drop-down box on the TVHeadend XMLTV tab.