I've heard GREAT things about Mederma actually - its used to minimize the appearance of scars, my GF used it on the scars on her arm from a bad burn and you can hardly see it anymore. They say it works great on stretch marks, too!
I already had stretch marks, now I just have more

so I'm going to try Mederma myself after pregnancy. It is one of those things you use afterwards to remove them though, I think.
Good luck! I hope you don't get any, but they pop up in the strangest ways... Not even kidding, baby kicked me really hard and I got one. And my skin is pretty elastic, it was just the way she kicked... Who knows! LOL