Added alignment support for named values.

string-format-extension.cs

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace Helpers
{
    public static class StringFormatExtension
    {
        // http://james.newtonking.com/archive/2008/03/27/formatwith-string-format-extension-method.aspx
        public static string FormatWith(this string format, params object[] args)
        {
            if (format == null)
                throw new ArgumentNullException("format");

            return string.Format(format, args);
        }

        public static string FormatWith(this string format, IFormatProvider provider, params object[] args)
        {
            if (format == null)
                throw new ArgumentNullException("format");

            return string.Format(provider, format, args);
        }

        // http://james.newtonking.com/archive/2008/03/29/formatwith-2-0-string-formatting-with-named-variables.aspx
        public static string FormatWith(this string format, object source)
        {
            return FormatWith(format, null, source);
        }

        public static string FormatWith(this string format, IFormatProvider provider, object source)
        {
            if (format == null)
                throw new ArgumentNullException("format");

            var r = new Regex(@"(?<start>\{)+(?<property>[\w\.\[\]]+)(?<format>:[^}]+)?(?<end>\})+",
              RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

            var values = new List<object>();
            string rewrittenFormat = r.Replace(format, delegate(Match m)
            {
                Group startGroup = m.Groups["start"];
                Group propertyGroup = m.Groups["property"];
                Group formatGroup = m.Groups["format"];
                Group endGroup = m.Groups["end"];

                values.Add((propertyGroup.Value == "0")
                  ? source
                  : DataBinder.Eval(source, propertyGroup.Value));

                return new string('{', startGroup.Captures.Count) + (values.Count - 1) + formatGroup.Value
                  + new string('}', endGroup.Captures.Count);
            });

            return string.Format(provider, rewrittenFormat, values.ToArray());
        }

    }
}