Jean jackets are such an essential item in a wardrobe. I've had a sort of obsession with them for a while (I even wore one to prom over my very fancy sequined dress from BCBG, but no there aren't any pictures because I was a weird teen with an aversion to cameras). I have a few different styles, but I think that before you go off on moto-style jackets and denim blazers, the classic jean jacket style is the one you really need.
Iconic Jean Jacket $39.90, Levi's.
When it comes to classic denim, I stick to the classic denim brands. My current favorite is from the boy's department at Gap Kids, I like the boxy fit and basic feel of it. This one from Levi's is an awesome price and there's nothing fancy about it, just a cool jacket in a dark wash that will go with everything (I am of the firm belief that denim goes with everything!). If you are petite, then Gap has a really cute version in a lighter wash that fits all the classic needs.
Chambray Trucker $39.90, Levi's.
Seeing as it's hot out though, I thought it appropriate to also provide a cooler lighter-weight option that will work on breezy summer nights. I love this version in striped chambray because #1, chambray is awesome but also because the lighter wash will look really great with white jeans, that other summer staple. If you're looking for more fashionable styles, Free People has a really great collection of vintage ones. Vintage stores and thrift shops are always loaded with denim jackets, so don't forget to scope those out for a truly unique one!