Who's got the biggest...
The h-index is a measure of a scholar's research productivity. It is defined as the largest number h such that the researcher has published h articles each cited at least h times.
A blog reader draws my attention to the Wikipedia article on the topic (the link above), which places me as the #5 economist, based on the REPEC ranking. Unfortunately, I cannot claim the honor.
The more commonly used data source for academic citations is the Social Science Citation Index, a private data base available online through many university libraries (including Harvard's). The SSCI is not perfect: cites to some journals, such at the Brookings Papers and the NBER Macro Annual, are wildly undercounted, because authors do not cite these journals using a consistent style. But this data base is the standard for counting citations. If you use the SSCI to perform a "general search" on an author, and then click on "citation report," the program gives you the author's h-index. Common names require some adjustment, but all the data you need are there.
After fooling around a bit, here are the economists (broadly defined) with the top h-indexes that I could find:
If anyone finds another economist in the 40+ range, post the news in the comments section.
In case you are curious, the Mankiw h-index is a mere 34.