Reference styles
Good guides to the different kinds of citations in each field: APA style is standard in Linguistics and many other social sciences, but MLA style is more common in English Literature.
http://www.dianahacker.com/resdoc/
http://www.wisc.edu/writing/Handbook/Documentation.html
http://hanyangwriting.tripod.com/citation/
MLA
http://owl.english.purdue.edu/owl/resource/557/01/
APA
http://www.library.ubc.ca/pubs/apastyle.pdf
Reporting Verbs (describing the research of others)
https://netfiles.uiuc.edu/k-lee7/www/kesl/writ/reportverbs.pdf
http://www.uefap.com/writing/citation/citefram.htm
http://iteslj.org/Techniques/Criollo-LitReview.html
Plagiarism
Excellent guide to avoiding plagiarism and references. It is especially good on problems with paraphrasing in science, which is often not included or treated too simplistically in other materials.
http://ori.dhhs.gov/education/products/plagiarism/
PDF version of the site
http://ori.dhhs.gov/education/products/plagiarism/plagiarism.pdf
A good collection of links on avoing plagiarism from UCLA
http://gsrc.ucla.edu/gwc/resources/citation-practices.html
Video presentation on using references and avoiding plagiarism (general academic writing).
http://www.unc.edu/depts/wcweb/esl/videos.html
Reporting verbs
Useful link on reporting verbs (verbs used to refer to other sources) but better for social sciences and not as useful for sciences.
http://www.writing.utoronto.ca/advice/english-as-a-second-language/referring-to-sources
Paraphrasing
How to use sentences from other papers and rewrite them in your own words.
http://www.monash.edu.au/lls/llonline/writing/information-technology/sources/2.5.3.xml
Tools to check for plagiarism