MBK 2-Skewer Diamond
You might already have some of the simple tools and materials required. Anything you don't have is easily bought. If not exactly what I used, then at least something pretty similar!
Probably the most important thing to get right is making and adjusting the bridle. This trips up so many would-be kite makers who are trying it for the first time! I've tried hard to make the instructions fool-proof in this area.
At 58cm (23") across, the MBK 2-Skewer Diamond Kite is small enough for kids and yet provides great light-wind flying performance for adults to enjoy as well.
The 2-Skewer Diamond has dihedral (the horizontal spar has a shallow V shape) and flies on a 2-leg bridle. Only a short tail is required, although long and colorful ones can be used for more spectacle in the air!
The video down there shows this latest version of the 2-Skewer Diamond on its very first flight, flying about on a fairly long line. Winds were gusting into the moderate range, causing the Diamond to loop occasionally.