Sad to say that Rollyo has closed down. Rollyo - short for 'roll your own' was a web based resource that allowed you to create your own search engine based on up to 25 websites that you defined for yourself. It wasn't necessary to register to use it, which made it very handy, and it was one of the sites that I pointed people towards.
However, all is not lost since there are two alternatives that you might want to consider - Google Custom Search Engines and Blekko. The Google option allows you to create a list of websites, folders or pages that you can then use as your search universe. Google will host the search engine for you, but you can also embed the code to create a nice search engine on your own site. Blekko lets you 'slashtag' the web by creating a self defined /slashtag that you can link to specific sites, and Blekko will limit its search to those sites. You can publicise the slashtag to friends and colleagues.
I'm not aware of any other examples, but if you do happen to know of any, please comment!