kuruman said:
you will need to go over the same basic material at the intermediate level before you might be eligible to apply to grad school
Emphasis on the "might." We occasionally get questions here from people who want to get into physics grad school without having formally studied physics at the undergraduate level, i.e. taken courses for credit, participated in research, etc. I don't remember ever seeing anyone report that they succeeded in doing this.
In general, in the US, graduate school admissions in physics requires:
1. suitable formal undergraduate coursework in physics, with at least a 3.0 GPA.
2. an acceptable score in the physics GRE
3. some research experience (not necessarily publications, but enough experience that you and they can tell you're cut out for research)
4. letters of recommendation from professors who know your work.
kuruman said:
The absolute minimum number of subjects at the intermediate level that you will need consists of Classical Mechanics, Electricity & Magnetism and Quantum Mechanics.
I would also include thermodynamics and statistical mechanics, which are sometimes covered in one course, sometimes two.
[added] As others have noted, Halliday/Resnick/Walker has been very widely used for "freshman physics" courses, for many years. I used the second edition (pre-Walker) myself when I was a freshman more than 45 years ago!
There are some other widely used books at the same level, but I suggest that as a supplementary resource you use the Feynman Lectures instead:
http://www.feynmanlectures.info/