The Sega Saturn analogue pad comes in many different variations as well as known under different names such as the Multi Controller, 3D Pad or NiGHTS Controller since that's what it was officially made for.  In Japan there were a few different packs for the analogue pad with the most common being this beautiful NiGHTS pack pictured on this very page.  Other packs include a Magic carpet one and pad only pack.  There maybe others such as a Space Harrier pack but I'm not too sure.

The Pad has a little switch near the bottom that changes the control from the analogue pad to the digital pad.  I'm not quite sure why both couldn't be used at once like on a Dreamcast pad though.  Around the back of the pad are two analogue trigger buttons which are great for racing games.  The actual cable coming from it is detachable which makes you think that Sega had some big ideas for this controller such as Air NiGHTS which was rumored.

The Saturn analogue pad is a must buy for all Saturn owners.  Not only does it make playing NiGHTS, Manx TT, Daytona Circuit Edition, Space Harrier, After Burner, Sky Target and countless other games much easier to play but it also feels great for normal 2D games including Capcom or SNK fighters.