Jumbo,
Your best bets for a great winter garden in the Lowveld are a variety of Aloes. Different species bloom from May through to about August and are great for attracting birds, insects and squirrels.
Secondly, plant the Common Coral Tree, Erythrina lysistemon. It blooms from June through to September and is amazing for attracting sunbirds, orioles, weavers, barbets etc etc. A really beautiful tree with scarlet flowers.It grows very easily from cuttings of the stem. let me know if you need, I can supply you with lots from my garden

The Impala Lily is also winter flowering and really stunning. I am sure everyone who knows the Park will know this plant.
A good tree to plant as well is the Ana Tree, Faidherbia albida. It is unusual in that it gets its leaves in winter and is therefore a great tree to have in your garden as it provides shelter for many animals and birds. However, be warned, it gets to enormous proportions.
The crane flower, Strelitzia reginae is anice shrub that flowers in late winter. It is not really indigenous to the Lowveld, but South African nonetheless.
Also a good suggestion, plant one of the indigenous figs - the best being ficus thonningi, the common wild fig. Again, plant it far away from any structure as the roots are invasive. Great for attracting birds, squirrles, genets etc.
I have one in my garden and on occassions have counted up to 15 different bird species in the tree at the same time!
Hope this helps