Suggestions for String and DateTime utility functions library using Extension Methods

Question

I'm writing a library of Extension Methods for String and DateTime utility functions in C#. What useful utility functions for String and DateTime might engineers want to be part of it? With your suggestions I can make it more cohesive and Collective.

Answer 1

public static bool IsNullOrEmpty(this string value){
    return string.IsNullOrEmpty(value);
}
public static string Reverse(this string value) {
    if (!string.IsNullOrEmpty(value)) {
        char[] chars = value.ToCharArray();
        Array.Reverse(chars);
        value = new string(chars);
    }
    return value;
}
public static string ToTitleCase(this string value) {
    return CultureInfo.CurrentCulture.TextInfo.ToTitleCase(value);
}
public static string ToTitleCaseInvariant(this string value) {
    return CultureInfo.InvariantCulture.TextInfo.ToTitleCase(value);
}

Trivial, but slighty nicer to call.