One of the most popular patterns I’ve heard of is the Baby Surprise Jacket by Elizabeth Zimmermann. It’s originally just the Baby Surprise Jacket, but the pattern was expanded to include child and adult sizes as well. I love this jacket because it’s knit all in one piece including sleeves – it looks strange until it “pops” and you see the sweater. This is why it’s called a “surprise” jacket.
It’s sold by Schoolhouse Press, a company started by Elizabeth Zimmermann and continued by her family. The second most popular Zimmermann pattern is her Pi Shawl, which is worked in the round and is easily customizable.
She also wrote a number of books and is famous for her “EPS” or Elizabeth Percentage System that says that each part of a properly fitting sweater for any size is proportionate to the other measurements. For example, if you calculate the number of stitches needed for the body of your sweater then you know that the sleeve needs to be 35-40% of that number of stitches. For a better explanation with some pictures, check out this Knitpicks Tutorial.