Aside from Panzer Dragoon (obviously), a Shining Force strategy RPG from the original developers could be awesome (imagine Shining Force III in high definition, made in Unity).
After that, maybe a Burning Rangers sequel?
Vectorman deserves another chance too. Lots of possibilities; his morphing ability could translate into many fresh gameplay styles limited only by the imagination. There was going to be a PS2 game, but it was cancelled.
I would also love to an isometric Landstalker/Dark Savior style game (it could use actual 3D graphics this time, but keep the isometric viewpoint). It would make sense to use a fresh IP so that there would be no need to get permission from Sega.