+1 for Jason's suggestions. I'd add that I need to be able to answer these questions within a minute of landing on your web site:
Well, since you asked, I sell an ebook, MicroISV Sites that Sell! ($19 USD, sometimes on sale for less) has received a good number of positive mentions. It's 90 pages on how to build, concept-by-concept, an effective, compelling web site for your small software business.
Here's a few links to consider:
WIIFM - a good article about defining your unique selling proposition.
Once you have that down, here's a good two part article on how to apply this to your homepage (the process the author uses to measure effectiveness is worth the read)
article: get visitors to read and remember your homepage
I recommend that you spend some time on this SEO forum: