Alternatively use some ASCII painting tool and use characters for the indexes.
Re: ASCII painting, recently I was looking into using an ASCII drawing tool like Monodraw [1] for creating ASCII maps. A format as portable as plaintext is appealing.
You can also use the drawn map as a template, and add random details (random variants of each tile). Also, you'll quickly find you want to use more sophisticated autotiling which handles multiple tile types meeting, and special cases. Here's an article about autotiling by defining rulesets which goes into more detail: http://www.squidi.net/three/entry.php?id=166
However, it's still pretty cool and refreshing to use. See e.g. Notch' Ludum Dare streams where he makes his levels in Paint.net: http://www.twitch.tv/notch/b/293084461 about 3:23:00 in.
