[The Colonel]

Someone used dwarves as elementals and IIRC early versions of RuneQuest had dwarves as machines*.

There was also the idea presented on the SoogaGames blog whereby dwarves, gnomes and halflings were all one species.

*I quite like the idea of going a bit Elder Scrolls with this - the dwarves, such as they were, backed themselves up onto a series of crystal matrices (perhaps to avoid a plague or something), some of which are installed in mechanical chasses so that they can perform routine maintenance of the mothballed dwarf holds. For whatever reason, the dwarves were unable to revert to "meat mode" and their species essentially no longer exists, leaving a series of "abandoned" dwarfholds for use as "dungeons" ... with some having mechanical guardians for PCs to fight. The crystal matrices, known as "dwarf power stones" are popular amongst the magic community who don't realise that they're consuming dwarven souls when they use them.
I'd couple this with a SoogaGames take whereby you have another "little people" species made up of those dwarves who got locked out of the holds when the grand backup occurred ... following the plague and civilizational collapse they know no more about the original dwarves than humans do and are more like hobbitses than dwarves.