I think every will agree that the best solutions is to create minisites and place ads (mostly from Google or Yahoo). You'll be surprise to see that it can generates some money! It's easy and fast. But still pay little...
Keep in mind that the smallest the better.
Content is king.
Go for niche market.
Always consider the location of your visitors.
You can even push a bit further by adding specific ads to your content (some website provides such services where advertiser place their ads and give you up to 15% of sales made from your website)
To sum up and give you an idea
********************************
5 pages with good content - written specifically for the US market - about back-pain when traveling by plane and with two nice ads to purchase special cushions and few Adsense
IS BETTER THAN
50 pages with general content on how to travel and poor MFA Adsense
My 2cents.
Lastly, you may want to search further in Webmasterworld because there are some great topics about parking and monetising parked domains.
*I have 10 parked domains at SEDO and earned only 1.83 USD in a year - not even enough to reimbursed the purchase of the DNS.
Then the domain should be optimised with searches that are going to be of interest to the web surfer. Some parking the optimisation is done for you, others you do the work. I have found parked.com will convert most genuine type-in traffic.
But to really answer your question the aim is to get domains with type in traffic.