Hi Stu,
In my Discus tank I have Rotala Macranda, Rotala Rotundifolia, Ambulia, Dwarf Sagitaria, Aponogeten Sp., Cryptocornes, Red Pinetree, Echinodorus Osiris and Echinodorus Amazonicus. They all grow well even at 30 Degrees Celsius. I have almost 1 watt per litre of light though and it will depend on your lighting setup and tank conditions as to what plants will do best, but the plants listed should give you and idea of what might work.
Cheers,
Matt