Some ideas…
1) A swashbuckler campaign is always good for light heartedness, allowing the PCs to swing from chandeliers, romance fetching women (or handsome men), toss off lots of one liners, etc.
2) Something like the swashbuckler campaign – have the PCs set up as some Robin Hood types that will allow them to tweak the noses of the powerful, rich and stuffy.
3)Or, have the PCs start off in what seems like a normal campaign, but have them zapped into another dimension only to discover that they are some strange futuristic world where a small rebel force is fighting off an evil empire and their soldiers in white armor, led by a powerful fallen knight dressed all in black.