Re format datetime to 7th November 2014

I don't believe there's any direct support for ordinals ("st", "nd", "th") within .NET. If you only need to support English, I suggest you hard code it yourself. For example:

string text = string.Format("{0}{1} {2} {3}", dt.Day, GetOrdinal(dt.Day),
                            dt.ToString("MMMM"), dt.Year);

(Where you'd write GetOrdinal yourself.) Note that this assumes you want exactly this format - different cultures (even within English) may prefer November 7th 2014 for example.

If you need to support all kinds of languages, it becomes very difficult - different languages have some very different approaches to ordinals.

Side-note: Even Noda Time doesn't handle this yet. I hope to eventually implement some CLDR support, which should in theory handle it for all locales. We'll see...