There are many ways to rank researchers, but rarely has one been adopted as fast as the h-index. It has been introduced by physicist Jorge E. Hirsch in August 2005, and is defined by h, with h works from an author having at least h citations. Compared to “raw” citation counts, which may put too much emphasis on a few much cited works, it highlights the trade-off between quantity and quality of research. Of course, like any research ranking criterion, it is imperfect in many ways and controversial to all but those who rank well. But it allows to highlight some aspects of research productivity.
RePEc has reported rankings according to the h-index since October 2005 for authors. There is also a variant for institutions and regions, where h is defined as the number authors with an h-index of at least h. Due to the large number of ties, how far an institution is from reaching the next h is also taken into account.
Quite naturally, the h-index can also be defined for journals and series. Starting this month, RePEc publishes such h-indexes: journals, working paper series (preprints), and all series combined. Obviously, journals and series with longer publishing histories are favored, and we hope this will have the side-effect of publishers making sure to have a complete listing on RePEc.
By the way, the overall h-index for all of RePEc is at 225 as of today.
Addendum (August 3): For authors, there is now also a Wu-index. This has been proposed by Qiang Wu and is defined in a similar way to the h-index, except that one needs 10 citations per paper. Due to the very large number of ties and zeros, this criterion is, however, not integrated in the overall rankings.
The RePEc Blog 
Great!
I guess h-weighted rankings of publications are next, which puts a premium on NBER membership.