http://www.tomeraider.com/
The software itself is shareware, but the ebooks for it appear to be free, although I haven't yet been able to download anything off their website.
There are different files you can download for wikipedia with 1.1 gb being the largest for it all! There's a version that only has the 1st paragraph of every entry (226 mb). All the files are searchable, formated for mobile viewing and updated!