Would you count the New Super Mario Bros. games part of the main Super Mario series? If they do, would we also count the Super Mario Land and Super Mario World 2: Yoshi's Island as well? How about New Super Luigi U?
Here's the main series accoriding to the Mario Wiki.
Super Mario Bros.
Super Mario Bros. 2 (JP)
Super Mario Bros. 2 (US)
Super Mario Bros. 3
Super Mario World
Super Mario 64
Super Mario Sunshine
New Super Mario Bros.
Super Mario Galaxy
New Super Mario Bros. Wii
Super Mario Galaxy 2
Super Mario 3D Land
New Super Mario Bros. 2
New Super Mario Bros. U
Super Mario 3D World
nice