In my lifetime:
Royle - Not sure, was only 5/6 years old. Maybe Gareth Taylor? Signed for a fair bit of cash and spent most of his time with us out on loan or in the reserves?
Keegan - Matias Vuoso, saw him play in the reserves at Hyde United a week or so after he'd signed and he looked good, but never saw him play for the first team. We really couldn't afford to waste the money in those days but that never seemed to matter to Keegan.
Pearce - Bernardo Corradi, at least Samaras scored a handful of goals. Corradi had those cool celebration routines but they were often performed for other players who weren't strikers and still managed to score more goals than him.
Sven - Rolando Bianchi, was alright for the first half of that season but dropped off quickly and was gone inside a year. Not sure why he suddenly decided to bugger off. Would have said Bojinov but that was nobody's fault really - a very talented player who couldn't stay fit.
Hughes - Tal Ben Haim, still get angry when I think about how bad he was. At least Jo scored the odd goal. All I remember about Ben Haim was him being completely wank from start to finish. One of the first City players I remember genuinely hating, dreaded every game he started.
Mancini - Scott Sinclair, we didn't want to sign him, he didn't want to come, and in the end he represented everything that went wrong with that 12/13 season. We needed a quick replacement for Johnson so we bought hastily and wasted £7m on him. At least Rodwell had two good games.
Pellegrini - Wilfried Bony, didn't have the worst scoring record but just never looked fit or even aware of his surroundings most of the time. Felt sorry for him sometimes because people really laid into him mercilessly but looking back I can't believe we held onto him for 18 months.
Guardiola - Nolito, started off well enough but soon lost interest in playing here and looked like he was deliberately trying to get himself in Pep's bad books by acting like a dickhead. Got himself in trouble for two headbutts in two games, complained about the weather, buggered off again.