The MRIcroGL, MRIcro for MacOS and upcoming MRIcron include the menu item Import/ConvertDICOMtoNIfTI - this will show you a graphical interface. You can set up your conversion and then drop the folder with the DICOM images onto the conversion window's toolbar. Whereas the old dcm2niigui had both the viewer and converter in a single program, with MRIroGL and MRIcron the graphical shell calls a command line program. The nice feature is that it shows you the terminal command used, so it is easy to set up a conversion with the graphical interface and then cut and paste the command into your favorite scripting language.