If you have at least 50 - 100 domains:

Park most of your domains at Parked for some of the best payouts. Apply for accounts at Sedo and  Active Audience if you expect your domains to make over $50 a week.  Both services have great looking landing pages.  Sedo & SedoPro are highly recommended for international domains. (Contact us to get an endorsement code for SedoPro - include your first and last name.)  Active Audience may improve search engine performance of your domains if you use their nameservers, but income there is down a bit lately.  

Consider Traffic Z for nice looking and flexible parking pages.  Check out other pages of this site for more on the strengths and weaknesses of these services.  

If you have less than 50 domains:

Park your domains at Sedo and/or Parked for almost instant results.  Apply for a Gold Key account and try some domains there too.  Some domains do dramatically better at Gold Key.  As mentioned above. Sedo is best for International traffic. Sedo and NameDrive use Google/AdWords ads, while Gold Key uses Yahoo/Overture.  Gold Key can provide search engine traffic, and their parking pages look better.  Their site takes a while to learn.

The video below provides information on a program that will help you learn SEO and domain development skills: