There is no such thing as a blu-ray free player. The codec license itself costs money. Unless I'm remembering it wrong, M$ was nice enough to finally include a native DVD codec in Vista-Win7, but the blu-ray codec is still new and therefore expensive.
Three options that I know of:
PowerDVD
Total Media Theater
WinDVD
The bundled players are often castrated in some way. The PowerDVD included in many player/software bundles can only play 2 channel sound.
You could try ebay. I'm sure there are a ton of fake copies for sale on ebay for $10-$30, but my original copy of PowerDVD came from ebay for about $10. I have upgraded it through Cyberlink twice now (~$60 each time). Whether or not that original copy was legit will be forever unknown, but it did upgrade to a legit copy!