Unfortunately, as you've already heard, iceberg lettuce is low in nutrients compared to other lettuces and greens. Consider Romaine lettuce, the kind with broad wrinkly leaves that is typically used in a Caesar salad. Romaine has six times as much vitamin C and five to 10 times as much beta carotene as iceberg. Salad greens like spinach, arugula, chicory, chard, or radicchio are even higher in many nutrients. When it comes to flavor, many lettuces and greens also have a lot more to offer than iceberg.
Some greens are peppery, others sweet, and still others have a slightly bitter flavor.
Greens also come in all kinds of shapes, which adds interest to a salad. For people used to the very bland flavor of iceberg lettuce, the assertive flavors of these darker leafy greens can take some getting used to. In that case, I suggest buying prepackaged salad greens at the market and mixing them with iceberg. Eventually most people find that they like the richer flavors of these other leafy greens more than iceberg. The strong flavor of dark leafy greens allows them to stand up to these other tastes, as well as to more complex and interesting salad dressings, such as balsamic vinaigrette or a tangy avocado and lemon dressing.