The Matrix boxset is still exclusive, Transformers (although that might be out in a couple of weeks on Blu,) Children of Men, V for Vendetta, Bourne Trilogy, Zodiac, Star Trek Season One, Hot Fuzz, Shaun of the Dead are some of the exclusives that come to mind.
Some think that there will be exclusives on hd for some time, but I disagree. I imagine that most of the studios will release their 'hd-exclusives' for Blu fairly quickly as the encodes are already done. I doubt that many will get re-encoded to take advantage of the higher standards, but apparently Transformers has both a Blu and an HD encode. I'll be interested to see the visual difference between the two if it's true.
One exclusive that I would probably pick up for $5 is Clerks II but they say that it looks soft. For that reason even though it's one of my favorite movies of the past couple of years I'd hesitate on buying it. At $5 it's a no-lose price though, even if they release a better looking Blu version down the road.