Ed Stark
I interpreted this as "who puts out game supplements that I like", which left me with James Wyatt, Ed Stark and Andy Collins.
If "cool" = James Dean, then I'd have to say Monte Cook. He went maverick and has been successful at it. Arcana Unearthed has a lot of good ideas, but as a designer he tends to complicate my job as DM. He has too many abilities and feats that are situation specific or only affect certain kinds of opponents. However, as an idea-man, Monte is top notch.
Ed Stark and James Wyatt seem to design abilities and feats (and PrC such as Iaijutsu Master) that are easy to DM,play and keep up with the power level of high level games.
And then, the most hated game designer........