I Need a Pencil: http://ineedapencil.ck12.org/
I Need a Pencil provides tutorials and practice activities covering all areas of the SAT. You can track their progress as you complete the sections. You can focus on a particular area or get help in all of the areas.
BLine Test Prep: http://www.blinetestprep.com/sat/
BLine provides a full-length SAT with explanations of the correct responses. You can stop at any point and finish later, and BLine saves your work; so it is not necessary to dedicate hours in one sitting.
My favorite tech blog, Free Tech for Teachers, provides a list of 10 great SAT prep sites and apps, mostly focused on vocabulary:
http://www.freetech4teachers.com/2011/05/10-sites-and-apps-for-sat-vocabulary.html#.UTTEZnxEhGg