My personal favourite is
Jagwear Virtual Designer NEW! 2008 Competitive Leo Designer
I personally don't have any leos from them(I can't afford them yet), but they make the comp leos for my club, and most of the comp girls use their practice leos. They have really nice designs, and you can even pick your colour choice completely. (For both comp and practice)
I also agree that GK Elite, while expensive, has some VERY nice designs.