You have the option with your cover letters of an indented-paragraph (semi-block) style, as shown in Dynamic Cover Letters and Dynamic Cover Letters for New Graduates, or a block style with a line of space between paragraphs (not shown except in the sample that follows).

Dynamic Cover Letters and Dynamic Cover Letters for New Graduates also show only two lines of space for your signature, while four lines should be allowed.

Follow this link for one example of a standard business letter format.

Follow this link for another example of a standard business letter format.

Follow this link to see some other free cover letter samples.