Are there any C# Bitcoin libraries and/or mining pool software packages?
Welcome

1) Here's an old project to start from

2) Here is the Bitcoin.it wiki entry on pool servers, including the derelict PoolServerJ

Mining is changing radically right now, with new hardware technology (ASICs) soon to be delivered which will likely increase the network hashrate by some orders of magnitude in the coming months. As a result, the protocols are changing to accommodate this increase, namely to stratum and getblocktemplate, if I recall correctly. 

Good luck!