Hi, I'm an ABD philosopher. The deepest and most interesting philosophical books are generally difficult and best accompanied by some form of instruction. This is true regardless of how clearly (e.g. Plato) or esoterically (e.g. Kant) written they are. There are some good secondary sources that can help but it's far preferable to be able to talk to an expert in a one-on-one or smallish setting. It would take a long t…
The above books are great, but unless you are really into philosophy I don't think you'd gain much from reading primary sources. (With the exception of Hume, he's brief and brilliant.) I think someone casually interested in philosophy would be better off reading articles from the Stanford Encyclopedia of Philosophy (plato.stanford.edu); and if a subject is particularly interesting then they can always go read some re…
I think that the Stanford Encyclopedia of Philosophy is very mixed. Often (not always) the articles spend a lot of time making distinctions among many views, without adequately explaining any of them at an introductory level, and at the expense of any sort of broad view of the issues. So like most philosophy reading it's most useful if you're already in a philosophy course or something like that.