I parked my domains at Go Daddy and Sedo, but I generate very little traffic. After trial and error, I found that WhyPark.com offers a nice service for free. While you may be limited on choosing templates and pictures, the Why Park will help you to build a fan following, as well as to improve your Google ranking.
Parked domains are basically worthless. If you don't receive repeat visitors, there is much you can do besides selecting the right keywords to make ad revenue. My blog barely receives any traffic, especially when I offer reliable information. Any person can transform a domain name into a powerhouse.
As for Why Park, this website will allow you to build a page for free using a dozen templates. You can write information about the website, as well as to select the keyword and phrases. Why Park offers some affordable plans that gives you access to additional services. In order to make money, you have to invest time into any craft. Some people are now deciding to auction their valuable generic domains that have aged like wine.
One piece of advice; be responsible with buying domains. Don't overdo it. You may have to let many domains go because the cost of renewing the registration for each domain will be enormous. If you plan to put work into the domains right away, you may generate the cost you paid for registration, and then have flexibility to sell the domain. For now, park the domains at Why Park. They allow you to write on the home page, which will likely add value to the domain. Invest time into a few domains you feel have potential to grow. Good luck.