You will need some 3 mm acrylic - a good place to try is a sign writer see if they have a scrap box.Cut to shape with hack saw, files and wet and dry paper to smooth the edges.Drill hole for ring. Attach keysThere are ways to personalize this simple ideaexample:Get some thick wire - about 1 or 2 mm - soft enough to bend with your hands. e.g. a coat hanger.Form some design or initials that will fit on you key ring.Put the key ring in the oven at about 130 - 150 deg C WATCH IT ALL THE TIME.Wait 5 or 10 mins until the acrylic softens & goes rubbery DON'T PICK IT UP WITH BARE HANDS HOT!!!!Put the wire on the soft acrylic and put the 2 between a couple of bits of wood big enough to cover the acrylic - Clamp TIGHT and wait until cool.When cool the design will be impressed in the acrylic.You can carry this a stage further if you feel inclined:Using a belt sander sand the face of the acrylic with the design until you have JUST remover the design.Put sanded acrylic back in the oven at 130 - 150 deg C.Watch the design reappear but this time it will be raised as the acrylic has a "memory" of what it was like before you treated it.People will wonder HOW you did it.