This is a fine non-recursive solution. There is however some duplication in the methods that can be removed.

Yes! Very nice!
Using for instead of foreach would add additional performance (foreach is quite slow in comparison to for).

Most of your solutions seems to fall into the "Clever" category.
It would be extremely hard to understand the code for a full application written this way.

That's the way you do it! Linq is powerful indeed.

Aaah, nice one. I attempted something similar but I had to add an extra filtering step to get rid of empty entries. Now I understand how I could have done it better!

This works. However, the way you build up the resulting string has really bad performance impact.
You should take a look at System.Text.StringBuilder.

I like this solution. Clear and easy to understand.

I agree with your solution, but why do you create the extra variable?

This is a nice solution. I noticed on the discussion page that some warriors thinks using sort for this kata is bad due to runtime performance (best sorting algorithms are O(nlogn)). However, I do not agree. Using sort here makes the code easy and intuitive to understand. If runtime performance is not an issue, simple code is far better than complex but fast code.