Here’s a few tools to get you started…
First figure out what you’re trying to sell. Use Google Trends and Google Keyword Tool to identify the keywords that someone would use to find your product. This should give you a vague idea of the market, if it’s growing or shrinking, and the set of keywords you’ll start with for your SEO and marketing copy.
Search the keywords from above on Google to see what kind of competitors exist. Take note of their branding, domain name, products/features available, and pricing. It’s good to know these things when figuring out what you need to do.
If it looks like they’re well-funded, take a peek on Crunchbase or Angellist to see if they have any notable investors and how much they’ve raised. It’s never a bad idea to do a quick Google New Search to see if they’ve been mentioned in any major publications.
Then you can use a site like LeanDomainSearch to see if there are any great domain names that contain any of your keywords. Perhaps you’ll go with a made up name, but this will get you thinking about a good name for your company. If you find a good one, you can use NameChk to see if it’s available on social networks.