Several RSS-enabled search and attention services have been cropping up over the last few days. I've not had the time to pour through them all, but will mention a couple (three in fact) probably worth trying our and keeping an eye on.
The first is by Chris Pirillo, called gada.be (via David Lovely). Scopes search against content types (news, blogs, etc) and topics such as 'geeky' and health. Features include export of results as OPML as RSS. There is also a FeedDemon plugin.
The next is Blogniscient a service Joel Ross describes as a 'Memeorandum-like' service. Articles are aggregated and and then clustered, rendered by topics (e.g. sports and science/tech) and can be filtered by type (news, blogs or 'freshness'?). No search - more of a subscribe and browse experience.
The last is a lesson in working the sphere of influence - the service hasn't even gone live yet getting a fair amount of buzz already (I've seen it mentioned in my RSS reader a few times in the last 24 hours. It's called Sphere: nice brand, nice domain and nice about Sphere page but have no idea if this blog search engine will be any good or not). Om Malik has more on the 'stealth-mode' start-up.