Don't just look at your competition's website and read a few articles. For a fuller view, try these information sources:
The competitor's website -- including hidden pages, all images, and any uploaded documents (PDF, DOC, XLS)
Former & current customers of your competitor
Win-Loss interviews with lost prospects & won customers
Job Postings on Indeed.com, LinkedIn, etc.
Patent & Trademark Filings
Hands-on experience with the competitor’s product or service
System Integrators, VARs, and Software Selection Consultants
The technical press
Industry analysts -- those Gartner and Forrester guys publish reports about how products compare, but they are usually extremely high level, focusing on "vision" and the size of the product's cusotmer base, rather than giving you a look at how a competitive product defines workflows.
Social Media-- Blogs, twitter, Facebook pages often contain product announcements and responses to customer complaints. YouTube, Vimeo & Slideshare are great for digging up old product demos, pitch decks, webinars, and "tech talks" by competitor staff. LinkedIn can tell you how many people list the competitor as their employer and the types of skills they have.
Website traffic analysis. Compete.com and Quantcast.com let you check out the traffic to your competition’s websites for free.
Trade shows - look over shoulders as they give demos in their booth. Attend sessions given by competitors.
"Secret shopper" consultants who will engage your competition's sales force.
Github - might give you insight into how many engineers there are, types of technology in use, etc.
Stack Overflow - their engineers might be asking technical questions in order to implement new use cases or use new technologies.
SEC Filings - if the company is public or is about to go public, their 10K and S-1 filings often contain a detailed list of risks to their business, who they view as competition, etc.