I had a friend ask me the same thing last week. I'd highly recommend
He gives small seminars at SMI in Palo Alto ($30 bucks and a great crash course in 2 hours!) and also one on one advice (spend a hour and he completely analyses your diet and gives you advice depending on your goals)
In summary, he advocates more small meals with each meal having ~65/20/15 carbs/protein/fat breakdown; with carbs being wholegrain. It's pretty intuitive but he's a great way to get up to speed quickly.
I second Angie's comments about Clyde! I took an athletic nutrition class from him back in 2005 and loved it. He does go a little overboard with the details, but that's merely because he is so passionate about it. I'm a triathlete, so I run quite a few half marathons a year, and one thing that I'll add is that nutrition during the race is also quite important. Assuming you carbo-load in the days prior, you'll have enough glycogen stored for the first ~60 minutes of exercise, but if you don't start taking in calories at that point, your performance at the end of the race can suffer. If you're finishing your race in 1:20, then water & Gatorade could do the trick, but if you're looking at 2+hrs, then I'd consider adding some calories to your drink. You body can absorb 200-300 calories per hour when exercising, and you want them spaced out over the hour, so I've had great success adding 2 gu's and a teaspoon of salt (or a bit less) to a waterbottle, then drinking that as I run. That way I get salt and calories with every drink, and therefore my energy level stays consistant and high. Once I adopted this practice I went from 10th or 12th in a race to top 5, purely from the nutrition. And I also recommend training with the same nutrition that you plan on using for the race. No surprises / nothing new on race day, or even on race week.
I hope that helps. I'm happy to discuss more if you'd like! Happy training & racing!