A simple, lightweight and maintainable way to output arbitrary CSV/TSV - keeps header names close to the column/value definition.

1. Usage.cs

// vars to be used inside column value funcs
DateTime utcnow = DateTime.UtcNow; 
const decimal VIP_SPEND = 1000000M;

var fields = new CsvDefinition<MyRecord>
{
  { "Username",      row => string.Concat(row.Prefix, ":", row.Username) },
  { "Email",         row => row.Email },
  { "Status",        row => row.TotalSpend >= VIP_SPEND ? "VIP" : "Pffft..., Peon" },
  { "Spend ($)",     row => row.TotalSpend == null ? "None" : row.TotalSpend.ToString("n2") },
  { "Year of Birth", row => row.Yob > 1900 && row.Yob <= utcnow.Year ? row.Yob.Value.ToString() : null },
  { "Enabled",       row => row.IsEnabled ? "Y" : "N" },
  { "Flags",         row => string.Join(", ", new string[]
                     {
                       row.IsDemo ? "demo" : null,
                       row.IsManager ? "manager" : null,
                       row.IsAdmin ? "admin" : null
                     }.Where(x => x != null))
  },
  { "Timestamp",     row => DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fff") }
};

IEnumerable<MyRecord> rows = someDataSource.AsEnumerable<MyRecord>();

using (var writer = new StringWriter())
{
	// perhaps write out some additional notes or headers
	// writer.WriteLine("# -- bof --")
	fields.Write(writer, rows, "\t"); // tab delimited
	// writer.WriteLine("# -- eof --")
	return writer.ToString();
}

2. CsvDefinition.cs

class CsvDefinition<T> : List<KeyValuePair<string, Func<T, string>>>
{
	public CsvDefinition()
		: base()
	{ }

	public CsvDefinition(int capacity)
		: base(capacity)
	{ }

	public CsvDefinition(IEnumerable<KeyValuePair<string, Func<T, string>>> items)
		: base(items)
	{ }

	/// <summary>
	/// Adds a Key/Value pair to the definition - used for easy object initialisation
	/// </summary>
	/// <param name="key">The name of the column/header</param>
	/// <param name="value">The Func to convert T into a string for the column value</param>
	public void Add(string key, Func<T, string> value)
	{
		Add(new KeyValuePair<string, Func<T, string>>(key, value));
	}

	/// <summary>
	/// Writes the CSV, outputs a header line, then iterates over rows, converting into column values using the defined func
	/// </summary>
	/// <param name="writer">The TextWriter to write the lines to</param>
	/// <param name="rows">The enumerable of T tothat represents the lines</param>
	/// <param name="delimiter">The string to delimit column values with. A single character delimiter isare also used to escape the value, multi-character strings are not escaped.</param>
	public void Write(TextWriter writer, IEnumerable<T> rows, string delimiter = ",")
	{
		if(delimiter == null)
			throw new ArgumentNullException("delimiter");
	
		char[] escChars = delimiter.Length == 1 ? new[] { delimiter[0], '\n', '\r', '"' } : new[] { '\n', '\r', '"' };

		string header = string.Join(delimiter, this.Select(x => escape(x.Key, escChars)));
		writer.WriteLine(header);

		foreach (T row in rows)
		{
			string line = string.Join(
				delimiter,
				this.Select(x => escape(x.Value(row), escChars)) // x.Value == Func<T, string>
				);

			writer.WriteLine(line);
		}
	}

	// adapted from: http://www.asp.net/web-api/overview/formats-and-model-binding/media-formatters
	static string escape(string value, char[] chars)
	{
		if (value == null)
			return null;

		if (value.IndexOfAny(chars) != -1)
			return string.Concat("\"", value.Replace("\"", "\"\""), "\"");

		return value;
	}
}