Here are two great websites:
http://www.askdrsears.com/html/3/T030800.asp "Feeding Toddlers: 17 Tips for Pleasing the Picky Eater" It has good ideas for introducing new, healthy foods to toddlers.
and
http://www.askdrsears.com/html/4/T040200.asp "ABC's of Teaching Nutrition to Kids" I thought this one was especially good because it teaches parents how to make learning about healthy food fun for kids. It talks about how to educate kids so that they make healthy choices on their own later on and so they know which kinds of food are healthy and why. The only thing I didn't agree with was that he suggested rewards, but everything else was pretty good advice. The article talks about referring to "grow" foods for kids.
He is old enough to help you plan meals, like "Do you want peas or greenbeans with dinner tonight?" If he helps you pick out veggies at the grocery store, he may be more willing to eat them. You can also give him different kinds of fresh fruits and veggies at the store to hold while he is sitting in the cart. Talk about what color they are, what they feel like, what he thinks might be inside, etc. Help him get interested in them. Also let him help you wash and prepare the food at home.
I have worked in child care for many years and I have never seen a kid in child care refuse the meal and ask for something else. This is because at day care, they know there are no other options. It sounds like you don't act as a short order cook, which is good. If he learns that what you are having for dinner are his only options, then he can either eat what you are having, or eat it later if he isn't hungry for it at dinner time. Just make sure he isn't getting "snack" food after dinner if he doesn't eat. This would teach him that he can just wait til after dinner to get something different to eat.
Also make sure he isn't eating too big of a snack in the late afternoon. If he is really hungry at dinner time, he may be more willing to try new things (you know that feeling when you're so hungry you'd be willing to eat almost anything? I'm not saying to starve him, or course, just make sure he doesn't ruin his appetite with a late snack). Also remember it can take more than 12 time of introducing a new food before some kids will get used to it. You could make a rule that everyone has to try one bite of each food on the plate, and if he doesn't like it, he doesn't have to eat any more. But at least he might try it.
It sounds like you don't, but try not to bribe him into eating his dinner with desert or treats. This would tell him that you have to eat the bad stuff to get the good stuff, and may put a negative association with eating healthy food.
Hope this helps a little