Hey JessieMay. Sorry your request sat unanswered for so long.
I use Power DVD. I'm not 100% sold on the image quality, but it's the one that seems to be the easiest to operate with the least amount of headaches.
There's a good chance that if you buy a retail Blu-ray player it'll come with software designed to read the format. Things get sketchy when you start buying OEM drives (a bare drive by itself, no retail packaging, manuals, cables, mounting screws, etc) or second hand and the person doesn't include the disk that they received with the drive.
There's a freeware program called PotPlayer by Daum. I was never able to get it to work on my home theater PC, which is why I had to drop some dimes on Cyberlink's software, but a lot of people are touting it as one of the best free programs that can read Blu-ray disk.
Let us know if you have any other questions or need any clarification.
For PC, I agree with Optix that PowerDVD is the best Blu ray player software. But for Mac, I use <a href="http://www.macblurayplayer.com/features.htm/">Macgo Mac Blu-ray player</a>. It is the first Blu ray player for Apple Mac OS X. And Pioneer BDR-XD04 is my favorite drive compatible with my iMac and Macgo.