Prohibited Constitutional Amendements?

As part of a sub-thread of the Second Amendment “right to bear arms” question it was suggested (incorrectly) that it would be more difficult to change or repeal the Second Amendment or other parts of the Bill of Rights (as opposed to amending any other section).

I do have a vague recollection from my Constitutional Law classes that there are at least some limitations on the Amendment process – i.e., you couldn’t eliminate either the Judicial or Executive Branches wholesale, and you can’t eliminate a state’s representation in the Senate (although you can tool with their delegation to the House of Representatives somewhat). Are there any heavy-duty constitutional scholars out there who can refresh my memory?

Article V:

The do it yourself version.