You’ll want to buy third-party RAM—it’s much cheaper than Apple RAM, and will work just as well. Don’t pay the $400 for the Apple RAM, it’s ridiculous—you can pay $100 for 4GB of ram at crucial.com.
With the pro, you get a separate graphics card, much bigger display, and your choice of matte or glossy display. And you get a lighted keyboard, a better keyboard (though you may have your own preference), and better build quality (in my opinion—but the Macbooks do seem to have some problems with the plastic cracking).
Is that worth it? It depends on your needs. I like the bigger screen, and since they both weight approximately the same, I’d much rather have the pro. I don’t do games, but I like the pro keyboard, matte display, and theoretically better build quality. The price difference (w/o the RAM, since they both start out with 2 GB) is much more than $100, but if you can afford it, and if you won’t be using an external monitor, I recommend the pro.