Added alignment support for named values.

string-format-extension.cs

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

namespace StringExtensions
{
    /// <remarks>
	/// http://james.newtonking.com/archive/2008/03/27/formatwith-string-format-extension-method.aspx
	/// http://james.newtonking.com/archive/2008/03/29/formatwith-2-0-string-formatting-with-named-variables.aspx
	/// </remarks>
	public static class StringFormatExtension
	{
		static readonly Regex NamedFormatRegex = new Regex(@"(?<start>\{)+(?<property>[\w\.\[\]]+)(?<format>:[^}]+)?(?<end>\})+", RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

		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);
		}

		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 values = new List<object>();
			string rewrittenFormat = NamedFormatRegex.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());
		}
	}
}