Ice Scan is a product search engine for consumer electronics, computer hardware and software, telephony, mobile phones, household appliances, and much more...

Ice Scan's search technology is based on Drupal's Apache Solr Search Integration,
http://drupal.org/project/apachesolr

Ice Scan uses the domain and i18n modules to build a fully multi-domain, multi-site and multi-lingual system. 12 languages, 11 domains, 11 Solr databases - all from 1 Drupal core using 1 MySQL database.

Also part of the series are:

http://ca.icescan.com - Canada
http://www.icescan.co.uk - United Kingdom
http://www.icescan.de - Germany
http://www.icescan.fr - France
http://www.icescan.be - Belgium
http://www.icescan.nl - Netherlands
http://www.icescan.in - India
http://www.icescan.it - Italy
http://www.icescan.es - Spain
http://jp.icescan.com - Japan

More domains will be added, as we scale it up to 100 million products. Products are imported using the feeds module, http://drupal.org/project/feeds

Top 5 most important Drupal modules to create such a site:

http://drupal.org/project/apachesolr
http://drupal.org/project/feeds
http://drupal.org/project/i18n
http://drupal.org/project/domain
http://drupal.org/project/views