1. Bertrand Russell - The Problems of Philosophy
A good introduction to the basic things which philosophers in the Anglo-American/analytic tradition worry about in logic, metaphysics and epistemology (primarily epistemology): induction, a priori knowledge, anti-sceptical arguments, and universals.
2. Hans-Georg Gadamer - Truth and Method
You know about the 'Continental' philosophers, right? All those wacky guys like Derrida. They are all a bit suspicious, right? Like, Heidegger was a Nazi, and Foucault spreads HIV. Yeah, gossip is great. A lot of this type of philosophy seems like bunkum - Alan Sokal showed that, right? Lots of waffly French dudes talking out of their ass, abusing science to basically support their political ideology. Gadamer isn't like that. He sets out to try and answer the question "how do we understand texts?" and rather than saying something goofy like "we just make up what we understand about texts" or that we deconstruct them by subjecting them to our ideological whims, ripping the book apart to suit whatever the passing fancy is. No, Gadamer tries to explicate how the reading of a book is more of a process that starts with pre-judgement - 'prejudice' in Gadamer's words. Such prejudice is natural and actually quite desirable. You do judge a book by the cover. To understand a book as a whole, you need to understand all the components which make it up. But to understand any bit of the book, you need to understand how it fits into the wider contest of the book. This 'hermeneutic cycle' is daunting, but the only thing you can do is jump on board.
3. Saul Kripke - Naming and Necessity
Kripke's book is on a slightly strange topic: how we use names. But how he deals with this is an interesting problem is a model of clarity and philosophical excellence. It has also been very influential - the way Kripke solves the problem with names led to other philosophers producing many so-called causal accounts of all sorts of things.
I'd post some more, but I've got to get the hell out of my hotel room and go to a philosophy conference...