About 10 years ago I got into starching my office dress shirts - a woman at work would OOOH and AAAH over them.
I recall trying to make my own liquid starch. I think I just dissovled corn starch in warm water. It worked well enough - I guess the "cooking" was completed during the ironing process, albeit with some flaking.
One of these days I'll try gmpayne's recipe.
As I recall from cooking... cornstarch is a bit unique in that it only thickens once. After first cooking it, it thickens. If you let it cool, and cook it again, it will thin. Weird.
Rice starch is available; I may try that someday. A super starch is lotus root powder. I bought some at an asian grocery a while back, and it thickens far more readily than cornstarch. It might make a good laundry starch too.