I've built Kurkesh, Onakke Ancient a couple times now, and always find him fun. Outside of the usual artifact shenanigans, my most recent build was planeswalker+proliferate, and that was rather exciting. I just wish they had more Liquimetal Coating effects.
Riku of Two Reflections is no where near as popular now as he used to be, but when he came out I built a budget deck with him, and all I can say is that Chancellor of the Forge with Parallel Lives gets into mathy territory real fast. (With only Rikku and parallel lives out, Chancellor makes over 100 goblin tokens. Add 26 goblins per extra pre-existing creature you control). I had a birthing pod chain in the deck, and I was looking for a step on the way to Craterhoof Behemoth (which had just come out, and was budget at the time), I eschewed the standard Avenger of Zendikar for the cheaper Chancellor. I quickly discovered that I never made it to my 8 slot. Chancellor alone was a game ending slot. Other fun things to copy over included Hellrider (Ever attack someone with 6 hellriders? It's fun), and Kessig Cagebreakers (attacked with 3 cage breakers, with 7 creatures in grave, and parallel lives out). My greatest game though, was probably where I managed to bouce chancellor and recast a few times, for over a billion goblins, then dropped a tripled craterhoof to reach something like 3x10^23 damage - non-infinite. Took a short while on the calculator to figure out the rough ballpark of damage.
I have been wanting to build a Chainer, Nightmare Adept deck for a bit now, but just haven't quite gotten started on it. He doesn't seem to be the most popular commander from that set of decks.
Depending on your group, just about any UR or URx commander can pilot a storm deck adequately well. You can adjust the commander based upon your desired difficulty. Mizzix/Kykar being easy mode, Tibor and Lumia being no help from the command zone mode.