Cover Letter Advice

GuardianJobs
It has pointers on the basics of cover letters, sample cover letters as well as what not to include in the cover letter.

Cover Letters that knock'em dead, Martin Yate (Adams Media Corp. - 7th Ed.)
This book takes an in-depth look at that other vital component of the job search (other than CV): the cover letter. Successful sample letters are included.

Job Star Central: About Cover Letter

Cover letters: Types and samples

Resume Resource: Resource for resumes and cover letters