What's a good, effective diet plan?

i have a wedding coming up in four or five months - not my wedding, but i'm in it- and i'm trying to get in shape and get the body i've wanted (and should have gotten years ago). i'm 24, 5'3"-ish and i currently weight around 136 lbs (134-137 if we're being technical). my doctor said my weight should be closer to 115, maybe a bit lower, for my body and frame size if i weren't to put on any muscle. (note: i know my weight is technically healthy, but i have joint problems that get worse when i get extra weight. extra muscle shouldn't be a problem and will help to stabilize and reinforce the problem joints). put another way, i want to lose about 20-25lbs of useless fat and put on a number of pounds of muscle. i'm trying to slim down, but also focus on toning up. i bought five workout videos which should arrive shortly :) and i plan on working out for about an hour to an hour and a half five or six times a week. it's mixed cardio and strengthening. what sort of diet plan should i follow? i've looked into a couple, but i can't decide which will help with weightloss, while still allowing me to be active and put on muscle. i need something a little more structured than 'eat healthy' and i have a fairly slow metabolism if that matters. i need a meal plan/eating schedule, too, if possible as i tend to wait too long and then eat too much or make poor food choices. i need structure ;) thanks so much for your help and i appreciate you taking the time to read the long post!