If you've got the time, I highly recommend taking CS107 at Stanford (for free): http://see.stanford.edu/see/courseinfo.aspx?coll=2d712634-2b....

I became incredibly comfortable with C -- memory management, handling pointers, having a very clear picture of how types are represented in memory -- after taking that course. The lecturer (Jerry Cain) is fantastic as well.

The course changed this year so I don't have any thoughts on the current CS107 offering if you plan on taking it through their online course offerings for pay. The lectures, syllabus, and materials on Stanford Engineering Everywhere (OpenCourseWare at Stanford) are all from the course I took two years ago.