The following kinds of downloads are available:
Database backup dumps
A complete copy of all Wikimedia wikis, in the form of wikitext source and metadata embedded in XML. A number of raw database tables in SQL form are also available.
These snapshots are provided at the very least monthly and usually twice a month.
Static HTML dumps
A copy of all pages from all Wikipedia wikis, in HTML form.
These are currently not running.
DVD distributions
Available for some Wikipedia editions.
Image tarballs
There are currently no image dumps available
"Okawix lets you download the whole content of Wikipedia, with or without images, so that you can browse it offline: Okawix is available in 253 languages and includes sister projects of the Wikimedia Foundation (Wikisource, Wiktionary, Wikiquote, Wikibooks)."
I know wikis are as popular with some educators as Al-Qaeda is with the CIA, however sometimes these portals and schools on Wikimedia sites can contain some interesting and useful information. I think so, anyway.