Olive oil or V6 oil (a blend of pure vegitable oils) you can get at http://youngliving.com/
After I had the baby I started putting the V6 Oil with few drops of Citrus Fresh Oil on my strech marks (which I have A LOT OF...) *the citrus fresh actually tightens the skin... and the V6 Oil helps lighten the stretch Marks... there is a VERY BIG difference in my stretch marks now... I mean... they are like 5 shades lighter... I have been slacking... but they are still fading day by day...
If you dont want to order anything from http://youngliving.com/- I would suggest at least going on there and reading some of the testimonials... I have one on there about my stretch marks... and the Gentle Baby Oil... that I use to give Meadow a massage before bed and it puts her right out...
If you cant afford anything on there... You can always just use olive oil!