I start with 10-10-10 and then bump up to a 20-10-10 if my plants look N defic. For Flowering, its like Bubba Kushman said, start with some 10-30-20 and go from there. Garden centers have tons ferts and shit. I just got some powdered local brand stuff that the old guy workin' there said was good for his tomatos.
I also agree with what he says about high P. It might seem like plants have no ceiling when it comes to certain nutes at certain times, but the chemistry going on in the medium often has mechanisms to deal with equilibrium going off balance...I was about to start talkin' about Ph, and phosphates...whoa