I have to agree with Melissa’s assessment of the feed search engines like Syndic8 and Topix. I’m not sure a dedicated search engine just for RSS feeds is necessary. Google Reader’s search function worked fine for me and, like Melissa, I found myself mostly just going to the websites in my favorites and either clicking their RSS feed links or copying and pasting their URLs into Google Reader.
I suppose you could save a little time by simply searching for a particular website’s feed on Syndic8. You wouldn’t have to search around for the RSS feed link on the site’s webpage (they’re never in the same place and some sites don’t even have them). Plus, they also proffer “featured” or “random” feed links on their homepages that may introduce you to a link you might never have purposefully searched for. And, they typically offer a way to browse through related feeds in case you’re looking for something new. Technorati is pretty impressive but Syndic8’s categories leave a lot to be desired (particularly because you have to drill down through several layers to actually get to a feed).
Technorati did a much better job of finding related feeds to blogs when I did a custom search for “raising chickens” than Syndic8 or Topix and the Bloglines’ search produced comparable results to Google Reader’s search.
All in all, I will probably end up doing what’s easy and familiar and continue to use Google Reader’s search function.