I have often recommended academic.live.com by Microsoft as a worthy rival to Google Scholar. At the very least, it was superior in its interface and sorting capabilities. Unfortunately, it provided much less relevant results in the humanities (focusing on more recent publications). Now Microsoft killed the service (along with Microsoft Books) which doesn't affect me personally since I rarely used it but it is bad news for the online research because Google Scholar could have used the competition. Hopefully, the technology will resurface somewhere else.

Live Search : Book search winding down Today we informed our partners that we are ending the Live Search Books and Live Search Academic projects and that both sites will be taken down next week. Books and scholarly publications will continue to be integrated into our Search results, but not through separate indexes.