I was reading Troy S.'s font rant, and it made me go open up Gnome Specimen and have a look at the serif fonts I have installed. I started going through them all, and these are the 5 best-looking serif fonts, in my opinion.
Yes, I know Liberation Serif has the "clunk" he's talking about, but I think for printed posters, the squared serifs look very nice. As I said in a comment on his post, Gentium is really my favourite. Its weight, the shape of the o's, the angle of the curves…they're just right. The only thing that can really give it a run for its money is Georgia, of which I have yet to find a GPL or CC version.