MRIcro is an excellent free viewer for medical images written by [http://www.sph.sc.edu/comd/rorden/ Chris Rorden]. It has many facilities, most notably ROI drawing and analysis.
See the [http://www.sph.sc.edu/comd/rorden/mricro.html MRIcro manual], [http://www.sph.sc.edu/comd/rorden/mritut.html MRIcro tutorial] and [http://www.sph.sc.edu/comd/rorden/faq.html MRIcro FAQ] - as well as other links on [http://www.sph.sc.edu/comd/rorden/ Chris Rorden's home page]. The MRIcro tutorial has instructions on creating a region of interest, and on how to prepare scans of damaged brains for spatial normalisation.
One of the features in MRIcro is the ability to display points on selected slices - such as maxima from various imaging studies. This is covered in the [http://www.sph.sc.edu/comd/rorden/faq.html#hotspot hotspot section] of the MRIcro FAQ, and also (for an older version) by our MricroPoints page.