SalesForce integration with .Net
Darren Terrell has a series of very good articles about SalesForce and .Net integration:
SalesForce integration with .net web services SOAP API
How to make .net query/insert/upsert/update/delete SalesForce objects.
SalesForce Integration with .net custom web services
How to make .net consume a web service created in SalesForce.
SalesForce Integration with .net callouts
How to make SalesForce consume a SOAP/REST web service created in .net.