Google  Scholar, at least amongst my peer group, doesn’t need an introduction.  The quality of its results,  the listing of authors on the left hand side, and one click access to “Recent articles” makes it my default search.  But I regularly dip into Live Search, ACM Portal, and (less often) CiteSeer to get a more comprehensive list of papers.

Live Search Academic, the offering from Microsoft, has a very neat interface that allows you to quickly preview the abstracts of the papers in your result set by hovering over them with your mouse.   In addition to searching by relevance (default), number of citations, and by author, you can group by an author (very useful), journal (neat), and conference (sounds useful .. isn’t).  The hover-over BibTex citation export is very quick and simple.

ACM Portal is most useful for me on campus, as the articles are downloadable when my IP is in the range that the Library uses.  As far as finding most recent research, Portal beats both Scholar and Live, hands down.