Saw this one while it still was in beta (I think), and it has certainly progressed ... I could have used it last year at a previous consulting assignment. Go to: http://www.jisc-adat.com/adat/home.pl ... you can compare academic databases, and it provides overlaps, etc. Very nice. (try comparing Scopus and WOS ... note the overlap, but also the wide range of unique journals to each ... there still isn't a global database that can claim to be comprehensive!

Of course, it would be nice to also see Google Scholar alongside as well.