Windows comes with a large assortment of TrueType fonts. Skewed a bit much towards the sans serif side but still pretty good.
My font of choice (despite trying Droid, Gentium, and most of the others suggested around here) remains Georgia. It's simply a wee bit darker than the others especially at the size I prefer.
For the PB360 interface font I favor Century Schoolbook and Lucida.
Just a tad taller at a given font size and since I favor the "Easy" bookshelf view on the PB360, they make the listings even clearer than other fonts.
Don't know how easy it is to get these days, but the old-time BITSTREAM TRUETYPE FONT PACK CD had a lot of premium-quality fonts for US$20 in the Win95 days. I found mine the other day and I spent a few hours checking out the various serif fonts in the deal. Lots of nice ones.
But I still ended up back with Georgia.