Modules that extend Igor and software products that use Igor:
SIDX allows Igor Pro to control scientific CCD cameras: Princeton Instruments, Photometrics, PCO/Cooke, Andor, SciMeasure, Spectral Instruments, DVC and Hammamatsu.
Iolite is Igor-based software for laser ablation ICPMS (inductively-coupled plasma mass spectroscopy).
Visual Integrity Technologies
Not strictly an add-on module, but Visual Integrity makes software to batch convert PS/EPS files to other formats such as XML-standard SVG, FrameMaker MIF and soon also PDF. See the PDF FLY page for more info.
Igor Pro 8
Igor XOP Toolkit
Igor NIDAQ Tools MX