I for one am waiting until one format is officially decided on once and for all. I know it seems like it's going to be Blu-Ray, but deep down inside I just wish it was HD-DVD.
Regardless, I think you have nothing to worry about in terms of selection of movies. The library is going to do nothing but grow from here on out. The only thing I'm not sure about yet is:
1. Will Sony release some cheaper players?
2. How about some players that have profile 2.0?
I would consider the PS3 but I would be getting it basically for the player, since I have my Xbox 360 for games and I have no interest in any games that are exclusive to the PS3 at this point... It all comes down to price. If the PS3 is the cheapest with the most features (and expandability) then I'll go for it.