Update: Commenter Steven D has pointed out a leap year error in calculating anomalies. The March anomaly is now 0.783°C, not 0.755 as I had earlier calculated. So the drop is 0.057, not 0.085.
The NCEP/NCAR index that I calculate from their reanalysis was down by 0.085°C in March, from 0.84°C to 0.755 (anomaly base 1994-2013). February was very hot indeed, so March is still the second hottest in the record, and of course the hottest March. The early part was part of a warm peak, over 1°C. Around 9 March it dropped to about the levels of January, and pretty much stayed there, slowly bringing down the average.
You can see the regional story on the active sphere map. In the date selector on right, just click the black square at the head of the March column. In N America, the W and mid US were cool, but a band of warmth around the East coast, and through Canada to Alaska. The Arctic was warm, of course, and also a band through East to central Asia, although E Europe was cold. El Nino is still there, and elsewhere mixed.
There are other similar results. Karsten's GFS is down by just 0.02°C; UAH is down about 0.07°C. Ryan Maue reports a CFSR drop of 0.07°C. In all cases, March is still close to second hottest month ever. And the BoM tells us that Australia had the hottest March on record, even including the hottest day (for the country) on March 2 (outside summer!).
I expect to have useful TempLS surface measures in a week or so.
The pattern of a Feb peak, with drop in March and then some recovery, was also shown in various records in 1998. In fact, the similarity is striking, though I think probably coincidental in detail.