A good idea is to check out websites that specifically review HD discs.
www.highdefdigest.com has a lot of very serious reviews for both formats and offers up forums specifically to discuss the discs from either camp. No BS or favoritism really present on the site so if you are a fanboy for one side or the other you aren't going to be happy with how even handed they are with both formats. But, their forums offer a fun 'smackdown' area designed pretty much for the fanboy in all of us.
If you really want to get the most out of your Blu-ray player then it is vital that you hook it up properly and ensure that you set your video output properly. With the PS3 this means using 1080p with a 10880p display, or setting the video output to 1080i. The PS3 has a few 'bugs' that forces it to downcovert HD video to 480p if you don't set the video output to 1080i or 1080p.
Recommended viewing: Tears of the Sun, World Trade Center, Mission Impossible III, Happy Feet.
It is important to NOT use many of the early releases, most notably HOFD or TFE as these are very well known to be poorly mastered discs and not reflective of what the format can deliver.
It is important, IMO, to view some of the animated flicks because it is a much better representation of what HD formats will truly be delivering as they mature more fully. Both sides really have nearly identical video playback capabilities so quality you see is more a limit of how well the encoding is done these days. I suspect that as HD digital movie cameras improve that we will see many more grain-free transfers made to video and the qualiity of live action match up to animation in short order.
I personally can't wait to see Cars. Or more honestly, someday to see The Incredibles or Nemo. Those should just be phenomenal!
EDIT: I have now read in S&V Magazine that THE Blu-ray player to buy is the PS3. It has since been repeated by Home Theater Magazine which says the PS3 looks identical in quality to the Pioneer Elite player... I have also heard from a couple of reputable sources the exact same thing: PS3 matches the highest quality sources out there for Blu-ray playback.