how can i create a link to a document in a library in c# using the object model in sharepoint 2010?
In fact, I would go with the following solution, if you are using the regular object model. I can't tell if that it would work also with the client object model.
Use the Content Type "Link To a Document" and use the following code to make it work. I had to do it for one of my projects, and it is definitely the way to go.
Check it here