start on my own or negotiate with the employer?
akamaka: Fear of violating contracts isn't a valid reason for not pursuing great ideas.  This is what Silicon Valley was built on.  If you have investor backing, you'll have help in handling the legal issues.A much better reason to try to sell your idea within the company is the fantastic support you'll have.  You're surrounded by people with deep knowledge of their domain, and it would be nearly impossible to find a co-founder with that level of experience.That being said, it's quite likely that the company leadership won't want to pursue your idea, even if they like it.  Maybe they're in a profit making mode, and don't want to invest and grow.  Maybe it would be difficult to get customers to adopt a totally new product (think of Coke or WordStar in the 1980s).It's also quite possible that some people love your idea, and others don't.  If you demonstrate the value of your ideas, and people who agree with you see that you're not being taken seriously, you've just found some potential co-founders.Who knows, there may be some guy in sales who's figured out a better way to market the product, and is also thinking of striking out on his own.