How 'new' are you going for?
http://www.amazon.com/gp/product/0789444550/sr=1-2/qid=1445464096/ref=olp_product_details?ie=UTF8&me=&qid=1445464096&sr=1-2
Also that anon that recommended the Republic is right, it's basically Plato's magnum opus, and it covers so many topics that he was the first to introduce to the study of philosophy.
>Ethics/Morality
This is the only linked book I haven't read but it seems concise to me:
http://www.amazon.com/gp/product/0812977785/sr=8-1/qid=1455465457/ref=olp_product_details?ie=UTF8&me=&qid=1455465457&sr=8-1
^^^Hopefully they don't try to liberalise Nietzsche.^^^
>from an objective viewpoint
Do you mean it tries to establish absolute morality or that it tries to examine it as a natural sociological phenomenon?
If the latter, go Dewey and Nietzsche's Genealogy of Morals.
Also, Chapter 9 of Beyond Good and Evil, especially section #260:
https://www.marxists.org/reference/archive/nietzsche/1886/beyond-good-evil/ch09.htm
>Linguistics
I've been wondering how to start this myself.
>>3585
I think he means how I mean it too. The scientific study of the structure of languages. How they work, how they evolve, etc.
>Idealism
A Treatise Concerning the Principles of Human Knowledge by George Berkeley.
>Time/Mortality
This instantly made me think about Heidegger's Being and Time, but that definitely isn't "starter" material. I suppose existentialism in general might fit this theme (Heidegger is often included among them)?
http://www.amazon.com/gp/product/0385031386/ref=olp_product_details?ie=UTF8&me=
Any criticism is definitely welcome.