As I explain to my students (I teach a course in Technical Communications, which includes business communications), you include your company name and title to give some credibility to your e-mail, you include phone numbers in case people need to reach you immediately, your website and other links as marketing for your business. I am going to add my Twitter tag.

On my cell phone I’ve shortened it (my name, company name, website, & cell phone number with a note that it’s from my android phone). My only admonishment is to be careful if you’re including your logo that you keep it small.

I know some people who routinely listserv email lots of strangers, and for security purposes leave their address out of their signature. In all other cases, though, leaving your address is useful and professional.