I recently discovered that there is some cycle parking within the Piccadilly Place Car Park on Whitworth Street Near Piccadilly Station. There's not that many of them, especially considering they are taking up the space of around 6 car spaces and only providing space for 16 bikes. I've no idea if it's free, but I couldn't see anything to do with charges for cycles or any kind of tickets on the bikes, so I presume it is free.
That London lot have raved recently about some cycle parking in a multistorey car park, but it seems us Mancs have half heartedly beaten them to it! ;-)
Apologies for the shit pictures. And don't be fooled by the lack of bikes, this was on a Saturday morning, presumably it looks a bit more packed on a weekday.