Ask Your Own People
Your customer service and technical support reps will know exactly what your product or service's shortcomings are and where marketing materials miss the mark. The questions that always resurface make wonderful topics for a series of blog posts covering troubleshooting tips.
Your sales reps invest their days talking to prospects and existing customers, forging relationships around the problems your product or services solves. Ask your star performers what information closes deals in your company. This information converts easily into quality content. In addition to posts and social media, consider creating a free ebook and offering it from your website in exchange for a subscription to your list.
Connect With Your Customers
Let your customers know that you value their opinions and wish to better connect with them. Grab a list of customers and search for them in social channels; then follow them in Twitter and circle them on Google+.
You can ask them if they prefer blog posts, Q&A's or YouTube video for solving problems. Listen to your customers and you'll hear what they'd like you to cover with your content. What are the things they're pleased with, with your product or service or those of your competitors, and what are they complaining about.
Be Active in Your Industry
Join LinkedIn groups for your industry or niche market. Subscribe to the RSS feeds and newsletters of industry leaders and your competitors. Subscribe to trade publications. You can find a lot of jumping-off points for your own content in what others in your industry are doing.
Don't Forget Web Analytics
Login to your company's analytics software and find the list of keywords people searched to discover your site. Expanding the content you offer around search terms that are already bringing you traffic can deliver a quick boost in visitors.