One common question is which objects are in the Sales Cloud vs. Service Cloud. Also, which objects overlap between the two. A little-known gem is the object diagrams found in the SOAP API Developer Guide.
With that sort of name, it is sure to scare off most administrators and consultants, but it is worth a click. You will find what are known as ERD Diagrams and they are broken out and available for not only Service (Support) Objects, but also Sales Objects, Task and Event Objects, and much more.
Here is a short video where I run through some of the diagrams. I also discuss some of the particular objects that you'll need to become familiar with as you study for the Consultant and Advanced Administrator Certification exams.