Straight saxes
From Oddwinds
Usually soprano (and smaller) saxes are straight, and larger ones are curved. But The L.A. Sax Company makes straight alto and tenor saxes, and near the middle of this page you can see a picture of a straight (red!) baritone. Granted, these instruments do curve a little, but not much. Conversely, there are some curved soprano saxes around, e.g. this one from Yanagisawa. (Category 3.)