One thing that all businesses must have is a quality set of business cards. It doesn't matter if your business is dog walking or dog food manufacturing, the surest way to signal to your prospective customers that you aren't a serious business is to hand them a handwritten piece of paper with your information on it. You must have a color business card, printed on card stock, in order to be a serious business.
So, you have two choices. You can purchase professionally printed business cards, either at a local store like Office Max, or you can buy online at a place like VistaPrint.com Both of them will require you to purchase at least 250 of the cards, and will run you between $30 and $80 per batch, depending on what options you have. Online sites like VistaPrint have business card templates that you can use to design your card before it is printed, which can be a nice benefit.
The other option is to make them yourself. In this case, you have three main options.
The first is creating yourself, printing yourself. This is the cheapest method, and you can usually print them in quantities of 10 or less at a time. Virtually all word processing packages have a business card template you can use, though they are often extremely bland. Open up Microsoft Word, select new, and select business card as a template. Type in your name and address in the few choices you get, and you're all set. A short trip to an office supply store will get you card stock paper, some especially made for home printers, and you're good to go.
The second method is to use business card software to create your cards. Several are available, some as freeware, that allow you to have a better experience in creating your own cards, including changing colors, designs, logos, etc. Often these will allow you to either print directly, or allow you to export an image that you can use to print. If you are a designer, you can use professional-grade image software like photoshop to create exactly how you want things to look, including the use of fancy techniques like fades and gradients.
Finally, you can do a blend of both. Use your word processor or software to design your card, but print them at one of the online shops, like VistaPrint. They usually allow you to upload the full image you want printed, and often you can get good quality cards for $20 or less, including shipping. Once you have your card uploaded, they generally store them for you, so that you can either order another one if you have an employee, or if you ever need more.