One way to get domains listed in search engines is to have lots of searchable content on the domain. This takes a lot of time and work. Some services have automated this process.
Why Park is one of the leading examples of a site that will add content to your domains. They will create sites full of content and allow you to place your own
ads on the site. WhyPark is a flexible alternative to domain parking. For around $100 you can create full-blown content-filled sites for up to 100 of your domains, and keep all of the ad
revenue (if you use your own AdSense or Yahoo account). Their templates are becoming more flexbile and more attractive as the system matures. Some Why Park pages have reached PR2 (Google PageRank) - a sign that Google is treating them as if they were full-blown websites.
Why Parknow has their own monetization option. They developed this system after Google AdSense canceled ads on many WhyPark domains, apparently because of "duplicate content". Yahoo ads still seem to work, and their new system will serve ads even if no other service will do so.
Some of the traditional parking companies also build pages with some content, but not full-blown articles. Keep in mind that the articles on such sites are usually pulled from public domain article sites. They are not unique, and their "duplicate content" nature may limit your rise in search engines.