Yahoo are BOSS
Yahoo have just opened up their search API’s (http://www.ysearchblog.com/archives/000599.html) to all-comers (this effectively legitimises http://www.topicala.com/). The service is called BOSS (http://developer.yahoo.com/search/boss/) and is free of rate limits and allows you to re-jig the search results how you want in nearly any type of application that.
It is a lot less restrictive than their original Search API but there are some limits: for instance searches have to be entered via a text box and not from a direct hyper link; you do get the freedom to present the results however you want. There appears to be no restriction on displaying adverts next to the results either.
It seems amazing what a company in apparent trouble will do to stay ahead of the game.