I'm not sure what direction to go in setting up communication between my iOS app and the database server. I was convinced till this morning that I should write a .NET web service but then I read about ASIHTTPRequest and now I'm lost what to use.
Any suggestions?
If by ".NET web service" you mean a SOAP interface, I strongly recommend against this. SOAP is a serious pain to manage on iOS. REST interfaces are much, much easier.
ASIHTTPRequest is no longer supported, and I don't recommend it for new projects. For REST protocols, I recommend MKNetworkKit or AFNetworking. I have a bias for MKNetworkKit, but both are good frameworks.