All of the first great philosopher's works (and some that used to be accredited as his but now aren't thought to be) in one book, what more could you want?

This volume actually has more of his truly great works than the first volume.

More famous than it's philosophical merit deserves perhaps, but it's so short you could read it in a couple of hours anyway.

Immensely important work on politics.

Locke, my favourite philosopher. This is one of his two great works.

Leibniz - wrong about most things, but still interesting and important. This contains a comprehensive selection of his most important shorter works.

Hume's most important work. Deals with many of the same issues as Locke's Essay (which was written before this), so it might be a good idea to read that first.

Kant's greatest work. He's difficult to read, but if you don't read Kant other philosophers will laugh at you. And possibly throw things.

Hegel is incredibly historically important. But if you thought Kant was difficult to read...

A reaction to Hegel. Not Kierkegaard's most important work, but short and useful.

Nietzsche's most important work, though not according to him...

Wittgenstein. Concise, often wrong, but he never fails to make you think. Fascinating.

With one space left I figured I might as well throw on a modern existential classic.