Hi M.. I think just about every parent goes through this stage with their toddler/preschooler. My little girl was a great eater until she turned 3. She's 4 now, and some days she is a piggie and some days she'll barely touch food.
Here are some things I had success with:
grilled cheese
string cheese
yogurt
macaroni & cheese (hmmm, lots of cheese, eh?)
pizza
pasta, with tomato sauce or butter
nutra grain bars (not the best nutrition, but they gotta eat)
baked chicken nuggets
pancakes & french toast with a little syrup & butter
fish sticks
Lots of whole grain options on the market these days that taste pretty good...pasta, pancakes, bread. Cereal may have sugar, but it's spray-coated with vitamins and he can eat it dry if he wants as a snack.
Good luck!
L.