To get to more than 1:1 magnification there are several options, but other than the Canon 65 macro (which you would be totally nuts to try underwater) there are no common lenses that are stand alone.
1. You can put a diopter on you current lens. The Canon 500 D is a good choice.
2. You can use an external diopter on your port. SubSee, Woody's diopter (nexus) and Macromate are some options.
3. You can put a teleconverter on your lens. Kenko/Tamron 1.4 gets you to 1.4:1 magnification at one stop less light, and the 2.0 diopter gets you to 2:1 magnification at 2 stops light loss. Unfortunately AFAIK there is no tele that works with the Canon 60 mm lens (EFS)
4. You can use an extension ring on your current lens, Canon makes a 12 mm that works with the 60 mm lens.
5. You can use several of these techniques together i.e. extension rings + tele + diopter.
Bill