Evidently, girls like boys who wear blazers. I have to say, they're on to something. A few quick rules. Fit, fit, and fit. Other than that, wear pretty much anything underneath it and you'll be okay.
Nom de guerre is the brand that, although spendy, will never really let you down. I normally prefer 3 buttons, but this 2 button blazer has a nice stance. This one I could wear everyday. Get it at Oki-ni.
I like gray. Plus everyone has a navy blue or black blazer. This Hope jacket is quite nice. Pick it up here.
This Opening Ceremony jacket may be navy, but I bet not too many of your friends have a knit wool blazer. The nice change of texture makes all the difference. Since I have a lot of jackets, this is the one I'd buy. You can buy it here.