Fastest way to convert a list of strings into a single concatenated string?

I have some LINQ code that generates a list of strings, like this:

var data = from a in someOtherList
           orderby a
           select FunctionThatReturnsString(a);

How do I convert that list of strings into one big concatenated string? Let's say that data has these entries:

"Some "
"resulting "
"data here."

I should end up with one string that looks like this:

"Some resulting data here."

How can I do this quickly? I thought about this:

StringBuilder sb = new StringBuilder();
data.ToList().ForEach(s => sb.Append(s));
string result = sb.ToString();

But that just doesn't seem right. If it is the right solution, how would I go about turning this into an extension method?