I'm totally sure this has been done to death, but I liked how this project turned out. We are doing a unit on transformations, and for the reflections portion, one of their homework assignments was this. In essence, they had to draw the x and y axes. They also had to draw the lines y=x and y=-x. Then they had to draw a word that was at least 4 letters long in the "first slice" (between the line y=x and the x-axis in the 1st quadrant). Then they had to reflect that word ALL around the lines and show some key points that they/I could check for accuracy.
I liked the "Reflection on the Reflection" piece I had them do in class when it was due (after they did a gallery walk). I asked them to write what they liked and disliked about the project and about their final product and if anything was challenging or easy or other such thoughts. It was enlightening to read their comments.
I didn't like that a ton of the final projects were such that their original word was "horizontal". That made it easier to reflect, I think. Maybe if I did this again, I'd say they had to do a "tilted word". I also think block letters may be a future requirement (for the challenge). I also think I may say that some letters have to have curves in them. Anyway, voila: