That reminds me of this article: http://nukemanbill.blogspot.com/2008/06/how-to-sell-your-sof... where the author discusses finding niches to sell big dollar software. Good stuff.
If you found a lot of value in this article, check out their website (http://www.horizonsoftware.com/). Although it's not interesting, unless you are interested in successful, multi million dollar software startups.