It's not quite clear what the original enquirer is looking for because it says 'sample library'. Do you mean a full range of musical instruments and other sounds, or do you mean piano only?
If the latter, then, as gvfarns says, the Ivory II, Pianotech and, above all, Galaxy Vintage D, are the most often quoted and praised here. All these are considered, to varying degress, good quality, up to date (and supported) technology, good value for money.
If you're talking about the former, then I'd recommend trying Kontakt from Native Instruments. You can audition their player and some of their sounds free here: http://www.native-instruments.com/en/products/komplete/synths-samplers/kontakt-5-player/
Personally, I'm quite fond of EWQL (orchestras, choirs, rock bands etc) but they are a little tricky to install and I haven't managed to download free auditions....you just have to buy it (they still deal in dvds/pre-loaded HDDs) Also you need to buy a 40 dollar security key called i-Lok to make it work at all (as you do with Ivory).
The internet seems littered with people moaning and complaining about their dreadful experiences with EWQL. This is a very small sample from Amazon (no sorting by me!):“ I shelled out the money for a product that I can't get to work and I can't get my money back. ” G. Monticello | 2 reviewers made a similar statement
“ Thanks for nothing. ” Anthony | 1 reviewer made a similar statement
“ EastWest doesn't even have a support phone number. ” C. Goldstein
.....but I rather like their panache. Anyone who causes so much ire must be worth investigating.