Assuming you're starting from scratch, here are some methods I use when brainstorming an initial list of post ideas:
1) What are all the topics related to the business? A business card printing company might also consider personal branding, networking, office culture or freelancing, design, professional events, typography, LinkedIn profiles, job-hunting, or sales relevant to their business, as well as business cards themselves.
2) What keywords are people searching for? Google's keyword tool, any Google auto-complete scraper, and a keyword-in-questions tool can help you find a bunch of related terms and phrases to generate ideas from. Google's keyword tool, which will also tell you how many times per month users search for each keyword, will help you qualify post topics as well.
3) Who, what, when, where, why, and how? Using the five Ws with your topics list is a good way to generate a bunch of ideas. Who uses business cards (what posts would interest each audience)? What do business cards have to do with personal branding? When have business cards made a big impact? Where can you find examples of good LinkedIn profiles? Why should you or shouldn't you list your phone number on your business card? How can you get a photo of yourself on your business card and have it not look like crap?
4) What are all the things we're learning? What are we producing that can be turned into content? Your company itself should be a rich source of blog ideas. Photos of the process, customer results, research you've done, etc. Your customers don't care a ton about you, but they are often interested in how the sausage is made if they can learn something useful from it too. Often when you're building a tool for a market, it's necessary to become an expert in that market -- write posts that showcase some of that expertise as you gain it.
5) Where can we find news, questions, and commentary related to our product? Google alerts, RSS feeds for any industry blogs, and twitter saved searches are some of my favorite tools for providing on-going inspiration for new posts.
Some ideas to use when you're facing a writers block for your niche: