MyAwardMaker is a free site with templates for certificates that you can download. They have a lot of different templates and they are organized by topic.
To create a certificate, you pick your template and then download it to your computer. You need to have Adobe Acrobat Reader (version 8.0 or later) to open the certificate. You can get Acrobat Reader HERE if you don't have it.
Once you open your certificate, you can then enter text into the open spaces and print it out. You can not save the certificate with the text added to it, but you can keep the template forever. You can also just print out the template and hand write the information.
Microsoft PowerPoint also has some certificate templates that you can use. You click on Design Templates and then go online. The site for the award templates is HERE. You then edit the slide and print it out.
I suggest printing them out on a color printer for best results and best appearance.