As of the latest dump of Wikipedia (1/7/2008), the entire content (in compressed form) can fit on a 4 GB thumb drive. There are tools available to decompress the content on the fly. In today's market, a 4 GB thumb drive is available online for under $20. The latest dump of Wikipedia (Jan. 7) is available at http://download.wikimedia.org/enwiki/latest/. The content file is enwiki-latest-pages-articles.xml.bz2. It is compressed with BZIP so that it shows a size of 3.2GB.