I think it depends on what you call "intimidating." If you mean it as someone a hitter is scared to stand in against, then it has to be the young Randy Johnson (ask John Kruk). If you view it as a guy that someone didn't want to face because they knew they would probably lose (as in intimitades the team/hitters just because he's that good), then Maddux and John Smoltz have to be on there. Maddux is hardly intimidating or a fireballer, but the fact that he could go through 9 innings in 85-90 pitches at times is intimidating enough. Smoltz throws hard and has a filthy slider and splitter, so it's going to be a tough at bat. He just hasn't been as wild or hit as many batters as others. As for me, I say Johnson and Ryan are the most intimidating though.
2000 Black GT
2V with a fuel pump and some other goodies
Touched by the hand of a tuning god -- Mr. Wilson