I would start with some water lilies, spike rush, blue flags, lizard's tail, duck potato, arrowhead, and giant bureed. I bought some of these at Lowes and some from Cardno and Spence. My recommendation is to contact the DNR and see if they have Partner funds available or at least could give you technical assistance (see link below). You might also consider if the best long term solution to the shallow depth would be to have the dam/drive rebuilt higher. I think you will likely need some grass carp to keep plants in check in such a shallow pond. The trick is not to put in too many and to have patience while they do their work. I have a lot of plants in my newest pond (too many), but I want to see how things develop over several years before I decide to add the grass carp, and if I do, I'll start with just 2 fish. My crayfish should also help when the population builds up. The best approach is to enjoy what you have while planning.
http://www.in.gov/dnr/fishwild/files/partner.pdf
