I've been recently working on a game, and I made an approach to make a tileset right now. Here it is.
(http://img135.imageshack.us/img135/2304/tiledk3.png)
C+C please. I'm aware of some issues by looking at it now, but It's too late to fix them. Maybe tomorrow. I'm also working on a simple Map Editor for my future games. For now all the tools are working besides the History system. It supports 64x208 tile sheets with 16x16 tiles. You can download it if you want, and you think it may help you test your tilesets. There are some known bugs but feel free to report.
Small documentation:
The config window should be self explanatory but there must be told that you should write all the names (Map and Tileset name) without the extensions of the files.
Tools:
Brush Tool - simply pick it up and draw;
Marquee Tool - use to select a rectangle;
Cut Tool - cuts selected area;
Eraser Tool - use it like the Brush Tool;
Copy Tool and Paste Tool - to use Paste you must first select area and press Copy button. After choosing any other tool, the Copy Tool will be released;
Move Tool - use to move selected area;
Crop Tool - use to crop the map after selecting desired space. It won't work if the selected area is smaller than the screen (edit space).
Undo and Redo doesn't work right now.
Use arrow keys to scroll.
Jogurt Map Editor
(http://img206.imageshack.us/img206/4646/jmeml9.png)
Download (New)
Redist. Pack needed (http://www.microsoft.com/downloads/details.aspx?FamilyID=9b2da534-3e03-4391-8a4d-074b9f2bc1bf&DisplayLang=en)