define a List like List<int,string>?

Depending on your needs, you have a few options here.

If you don't need to do key/value lookups and want to stick with a List<>, you can make use of Tuple<int, string>:

List<Tuple<int, string>> mylist = new List<Tuple<int, string>>();

// add an item
mylist.Add(new Tuple<int, string>(someInt, someString));

If you do want key/value lookups, you could move towards a Dictionary<int, string>:

Dictionary<int, string> mydict = new Dictionary<int, string>();

// add an item
mydict.Add(someInt, someString);