In-flight meals have come a long way since the days when your options were the regular meal, or the kosher meal. Many major airlines now offer many other choices, based on dietary habits or custom.
It will depend on the airline, the length of the flight and your seat class, so you might want to ask about options. You can get meals that are vegetarian, low fat, diabetic, or gluten-free. And for religious restrictions, there are Muslim halal meals as well as Jewish kosher.
Many people will choose the vegetarian option, even if they are meat-eaters as the food is often healthier and fresher.
To check on your airlines options and food quality, take a peek at airlinemeals.net for a whole gallery of passenger photos and reviews.