I posted this on another thread, but wanted to post it here as well since this is a sticky thread.
For vegetarians...
Both parks have soft pretzels, fresh fruit, ice cream, etc. available through-out the parks.
IOA
Cinnabon
Confisco Grille - Nachos (order w/o beef), vegetable pizza, salads, PB&J (on kids menu) & cheese pizza (also on kids menu)
Cafe 4 - Cheese pizza, veggie pizza, fettuccini w/garlic cream sauce, pasta salad, breadsticks, ceasar salad & minestrone soup
Captain America Diner - Fries, onion rings & salad
Blondie's - Veggie sandwich, cream of tomato soup, salad, coleslaw & potato salad
Comic Strip Cafe - Cheese pizza, veggie pizza, fettucine alfredo, PB&J (on kids menu), veggie stir-fry, nachos (order w/o meat), coleslaw, fries, onion rings, salad, breadsticks & pasta salad
Wimpy's - Salad, fries & onion rings
Pizza Predattoria - Cheese pizza & caesar salad in pizza crust
Burgers Digs - Fries & onion rings
Thunder Falls Terrace - PB&J (on kids menu), roasted corn, roasted potatoes, black beans, rice & fries
Enchanted Oak Tavern - Salad, fries, mac & cheese (on kids menu) baked potato, corn muffin & corn on the cob
Fire Eater's Grill - Salad & fries
Mythos - I think their menu changes
Circus McGurkus - Cheese pizza, alphabet soup, salad, corn on the cob, mashed potatoes, biscuits & honey, breadsticks & fries
Green Eggs & Ham - Green eggs & hamwich (w/o the ham, so I guess it's just a green egg sandwich, although it does have cheese on it), salad, fries & onion rings
Universal Studios
Beverly Hills Boulangerie - Salad
Cafe LaBamba - Salad, fries & corn on the cob
Mel's Drive-In - Fries & onion rings
Animal Crackers - Fries
International Food & Film - Cheese pizza, minestrone soup, breadsticks w/marinara sauce, fries, mashed potatoes, corn on the cob & stir-fry veggies
Monster's Cafe - Cheese wood fired pizza
Finnegan's - Potato & onion webb (thinly sliced potatoes & onions, beer-battered & fried), garden burger, mac & cheese (on kids menu), grilled cheese (on kids menu) & PB&J (on kids menu)
Louie's - Cheese pizza, garden veggie pizza, fettucine alfredo, salad, minestrone soup & breadsticks w/marinara sauce
Captain Quint's & Midway Grill - Coleslaw & fries
Chez Alcatrez - Nachos (order w/o meat)
Lombard's - Portabella mushrooms (fried in a tempura batter & served w/italian dressing), fresh fruit (w/cottage cheese or raspberry sorbet), garden burger, bravo pasta (cheese ravioli w/marinara, pesto & garlic cream sauce) & linguini w/marinara sauce (on kids menu)
Richter's - The fault line (garden burger), fries & fresh fruit
City Walk
Margaritaville - Volcano Nachos (order w/o chili), quesadillas (order w/o chicken or beef), vegetarian pasta, portabella mushroom sandwich, veggie burger, salad, fries, onion rings, mashed potatoes, sweet potato chips, steamed veggies & roasted red potatoes
Hard Rock Cafe - Southwest nachos, homemade HRC nachos, potato skins (order w/o bacon), salad, portabella mushroom sandwich, veggie burger, veggie fajitas & fire roasted vegetable pasta
Both of Emeril's restaurants have veggie selections. You can see them at Emerils.com. I'm not sure what Nascar & NBA City have to offer in the way of vegetarian meals.
If I forgot something, added something that no longer exists, etc., please feel free to let me know.