The purpose of a logo is to "brand" your company, make it immediately recognizable to your existing and potential customers.
Do you have a logo?
Your logo should be a simple graphic representation of your business that is used consistently on all of your printable material. Logos are not just for business cards.
They can and should be used in all advertising, letterhead, invoices, signs, promotional items such as pens, t-shirts, coffee mugs and of course on your website.
Every business should have a standard package that includes it's logo on a business card, stationery, invoices, and a display ad.