Hmm. I am pretty lucky we don't have a picky toddler.
But she's a low-volume eater, so that's a problem in itself. Her weight picked up once she started school, they give her more calori-dense stuff, which I don't really mind but I don't really eat it at home, and we give her more healthy stuff (lots of fruit and veggies, lots of high quality protein, not a lot of refined carbs.)
We've found soups to be really great. I make the weight watcher's zero point soup for myself and puree it. She loves a few tablespoons a day! I boil it down with a bouillion cube and add a bunch of fresh and frozen veggies, like kale, chard, leeks, broccoli, mushrooms, cabbage and cauliflower, onions and garlic, and spike it with v-8 type juices. When you puree it, it is very green and velvety, so we call it Green Velvet Soup. Sometimes I put noodles in it for her.
Tempura veggies are really palatable and my daughter will now eat steamed carrots and steamed broccoli. Our daughter will also eat pasta, and we get the high protein/high fiber version from Barilla. It really boosts the protein consumption. Typical meal for our kid: barilla pasta with light sauce, apple slices, steamed broccoli. If she's still hungry, she eats tofu or drinks a yogurt. We're not vegetarians, but our kid won't normally eat meat. Chicken legs, on the bone, and last night's steak for some reason, tends to be the limit of her meat palate, but we still offer things with meat in them to her.
Toddlers really seem to love to dip things, so we give her toast fingers or pitas with hummus, organic strawberries with yogurt dip, chips and salsa and that sort of thing for snacks.
The biggest thing seems to be that you just have to offer foods many times. And praise them like mad when they try it, even if they spit it out.
It just takes awhile to get used to some tastes and textures, I guess! I didn't start eating mushrooms until I hit my 20s!