GradSchools.com has a search tool to help you find degrees in your field of interest (in any field!), as well as various FAQs and advice about graduate schools and graduate programs. If you're really not sure where to start looking for advanced degrees, this might be a useful place!
The American Chemical Society has a very useful page with advice for prospective graduate students and a "graduate school reality check" booklet that applies to students in any major, not just STEM majors!
The Educational Testing Service website has everything you need to prepare for, register for, and take the GRE.
The Council on Undergraduate Research offers many resources to undergraduate students, from job and internship boards, to advice on how to make resumes and CVs, to bigger-focus advice on things like finding research opportunities.