I love oatmeal. So much in fact, that it used to compromise the base for 3 of my 4 meals in a given day. While there is worse foods to have as a main component of a diet, I was certainly missing out.
Oatmeal is a great source of soluble fiber. This is the fiber that can lower cholesterol and control blood sugar. Besides oatmeal, legumes (think black beans, humus) are good options too.
However, the other type of fiber is insoluble fiber. This is the type of fiber that helps with regularity (always a good thing). Sources here are your vegetables and whole grains.
Both are important and should be included to hit your 20 to 35 gram intake for the day. Look for carb sources that have at least a couple grams per serving. Also, make sure that you get your water too as fiber needs this to function properly as you don't want to clog the pipes!