HostedBy is a project mainly written in Java, it's free.
Java-based tool to parse bookmarks and produce an ordered list of hosting providers.
HostedBy was an exercise in Java programming. It inputs a file containing a set of bookmarks and performs a whois look up on each unique domain. The hosts are then listed in descending order of popularity.
Crude but effective.
NB: This works with a bookmark file produced by Safari. It has not been tested with any other browser's bookmark export.