If you're in the mood for something light, see IPS Advisory, Inc.'s Plain Language Risk Disclosure for their IPS Millenium Fund. This site has links to tons of resources for workplace writers. This comprehensive site contains often updated links to resources for writing at work. This site is devoted to improving communication between government and the public. It contains lots of resources, including sample documents.
OWLs contain information for writers of all types.
This site includes links to lots of language exercises and advice about different topics of interest to non-native English speakers. This site gives you the basics on how to find information online. This site is a comprehensive source written specifically for undergraduate business or technical writing students. There is a handy little table which summarizes certain common characteristics among the search engines, some general search tips, and cross-references to other useful articles. Teaching Undergrads WEB Evaluation by Jim Kapoun.