Вот мой контроллер:
[HttpPost]
public ActionResult Index(HttpPostedFileBase excelFile)
{
/*Somewhere here, I have to save the uploaded file.*/
var fileName = string.Format("{0}\\{1}", Directory.GetCurrentDirectory(), excelFile.FileName);
var connectionString = string.Format("Provider=Microsoft.Jet.OLEDB.4.0; data source={0}; Extended Properties=Excel 8.0;", fileName);
var adapter = new OleDbDataAdapter("SELECT * FROM [workSheetNameHere$]", connectionString);
var ds = new DataSet();
adapter.Fill(ds, "results");
DataTable data = ds.Tables["results"];
return View();
}