I'm not going to talk about really old players that I never saw, but I'd say some of the most fearsome bowlers in recent times have been Allan Donald (there was a series against England in 1998 where he was truly terrifying), Courtney Walsh & Curtly Ambrose, Waqar Younis and Wasim Akram. For a short time, Andrew Caddick was feared by a lot of teams... I remember in 2000 he absolutely tore West Indies apart. I'm not sure if anyone has mentioned him, but when he is fired up, I think Flintoff is one of the most lethal bowlers around... I think he's very underrated as a bowler. Shoaib's pace is truly terrifying, but he is so inconsistent that I don't think batsmen are ever that scared of him, they know that they will always be able to get a few runs off him.