Blog search, the next step

Right now most of the blog search tools, Technorati, Blogpulse, et al, are reasonably good at finding the most recent links or most recent postings on key words. But what if you want to search the archives? What if you want to know who was linking to you or your clients’ site in January 2005? Currently I know of no good way to do that sort of search. Anyone with an idea is encouraged to post it in the comments.