Making money on parked domains

Almost two years ago, I got excited about parking domains. I took about a dozen of my domains and parked them at a service called TrafficClub. I built some links to them and waited for my retirement fund to start building, all by itself.

A week later, I'd made ..... $.03! I built a dozen or so links to them and waited another month. A nickel. And after a few months, I lost interest, starting slowly moving domains elsewhere when I needed them, and forgot about it.

Last week, I got a check - $105 - from some service that I'd never heard of. It turns out that TrafficClub got rolled up into some other big group and one of my domain, over the previous 90 days, started making money. Can you guess which one? The winner gets a Time4Learning coffee mug.

http://www.california-home-school.com/
http://www.californiavirtualacademy.com/
http://www.florida-home-school.com/
http://www.florida-home-school.org/
http://www.gifted-student.com/
http://www.gifted-student.org/
http://www.home-school-online.com/
http://www.home-school-resource.com/

Ps - Any advice ? Should I leave them there waiting for another windfall? Is it a one time deal or will it keep paying it? Should I move the others elsewhere and give a different service a try? What service? Would building links, perhaps with proper anchor text and title tags, make a big difference?

Here's some more that have been parked:

OK, I haven't made any money but I'd like to.....Here's some more that I parked for money at GoDaddy. It's an area where I've been frustrated by a dirth of info so I hope to provide great articles and forums over time. Right now, I'm busy so I'm parking them...

Credit Card Vendor info
Credit Card Vendor mobi
Credit Card Vendor net
Credit Card merchant account - CREDITCARDMERCHANTBLOG.COM
Credit Card merchant - CREDITCARDMERCHANTSITE.COM
Credit Cards online - CREDITCARDSONLINEBLOG.COM
credit cards merchant accounts - THECREDITCARDMERCHANT.COM