Try the hypertext version of Websters dictionary.
If you know your word but want its sibling, try the searchable Roget's Thesaurus.
If you need to cite the source of certain words, go to the online MLA and APA citation guide.
You can check the UT Undergraduate Writing Center's handout collection, including information on
There is an extensive collection of writing exercises and guides at The Purdue University On-Line Writing Lab, including information on