Your slogan should be just a sentence or two that conveys to a customer what it is you're going to do for them. Creating a slogan is tough! Don't be discouraged if you don't have one or can't some up with one right away.
There's nothing wrong with simply stating what you offer, like "Website Design and Internet Consulting." You can also talk about the way that you help or concentrate on a specific service.
If you don't have a slogan, consider having a contest on Facebook or Twitter for your new business. It will generate some interest and hopefully give you some good ideas.