Thought this might be handy for someone, this is an extremely simple CSV export class that I needed. Features:

• Extremely simple to use
• Escapes commas and quotes so excel handles them fine
• Exports date and datetimes in timezone-proof format

Without further ado:

using System;
using System.Data.SqlTypes;
using System.IO;
using System.Text;
using System.Collections.Generic;

/// <summary>
/// Simple CSV export
/// Example:
///   CsvExport myExport = new CsvExport();
///
///   myExport.AddRow();
///   myExport["Region"] = "New York, USA";
///   myExport["Sales"] = 100000;
///   myExport["Date Opened"] = new DateTime(2003, 12, 31);
///
///   myExport.AddRow();
///   myExport["Region"] = "Sydney \"in\" Australia";
///   myExport["Sales"] = 50000;
///   myExport["Date Opened"] = new DateTime(2005, 1, 1, 9, 30, 0);
///
/// Then you can do any of the following three output options:
///   string myCsv = myExport.Export();
///   myExport.ExportToFile("Somefile.csv");
///   byte[] myCsvData = myExport.ExportToBytes();
/// </summary>
public class CsvExport
{
  /// <summary>
  /// To keep the ordered list of column names
  /// </summary>
  List<string> fields = new List<string>();

  /// <summary>
  /// The list of rows
  /// </summary>
  List<Dictionary<string, object>> rows = new List<Dictionary<string, object>>();

  /// <summary>
  /// The current row
  /// </summary>
  Dictionary<string, object> currentRow { get { return rows[rows.Count - 1]; } }

  /// <summary>
  /// Set a value on this column
  /// </summary>
  public object this[string field]
  {
    set
    {
      // Keep track of the field names, because the dictionary loses the ordering
      if (!fields.Contains(field)) fields.Add(field);
      currentRow[field] = value;
    }
  }

  /// <summary>
  /// Call this before setting any fields on a row
  /// </summary>
  public void AddRow()
  {
    rows.Add(new Dictionary<string, object>());
  }

  /// <summary>
  /// Converts a value to how it should output in a csv file
  /// If it has a comma, it needs surrounding with double quotes
  /// Eg Sydney, Australia -> "Sydney, Australia"
  /// Also if it contains any double quotes ("), then they need to be replaced with quad quotes[sic] ("")
  /// Eg "Dangerous Dan" McGrew -> """Dangerous Dan"" McGrew"
  /// </summary>
  string MakeValueCsvFriendly(object value)
  {
    if (value == null) return "";
    if (value is INullable && ((INullable)value).IsNull) return "";
    if (value is DateTime)
    {
      if (((DateTime)value).TimeOfDay.TotalSeconds==0)
        return ((DateTime)value).ToString("yyyy-MM-dd");
      return ((DateTime)value).ToString("yyyy-MM-dd HH:mm:ss");
    }
    string output = value.ToString();
    if (output.Contains(",") || output.Contains("\""))
      output = '"' + output.Replace("\"", "\"\"") + '"';
    return output;
  }

  /// <summary>
  /// Output all rows as a CSV returning a string
  /// </summary>
  public string Export()
  {
    StringBuilder sb = new StringBuilder();

    // The header
    foreach (string field in fields)
      sb.Append(field).Append(",");
    sb.AppendLine();

    // The rows
    foreach (Dictionary<string, object> row in rows)
    {
      foreach (string field in fields)
        sb.Append(MakeValueCsvFriendly(row[field])).Append(",");
      sb.AppendLine();
    }

    return sb.ToString();
  }

  /// <summary>
  /// Exports to a file
  /// </summary>
  public void ExportToFile(string path)
  {
    File.WriteAllText(path, Export());
  }

  /// <summary>
  /// Exports as raw UTF8 bytes
  /// </summary>
  public byte[] ExportToBytes()
  {
    return Encoding.UTF8.GetBytes(Export());
  }
}