Credibility Tell people who you are and how they can contact you. People are not going to buy from somebody who works out of the trunk of their car. Show them your postal address. Show them your phone and fax numbers. Register your virtual domain name.
People are more comfortable buying from established companies.
If you've been marketing software for a while, tell them how long you've been in business. Get rid of banner ads that are unrelated to your site. Eliminate the links to your local weather and sports franchises. Remove the political, religious and social references from your site. By including off-topic information on your software site, you're diluting both your social and your software message.