Hi
Off the top of my head:
IBM
Samsung
Siemens
TIA - slow, unreliable!!! Technology Innovation Agency (government).
Woolworths, SABreweries etc may be interesting - my agenda here is that I think these are companies who could get behind hacking and biology (biology as in food, beer, water, sustainability stuffs - so this is a rather personal agenda I have...)
Also, Silicon Cape might have some advice or links, networks to share.
Georg Lerm from Arduino Cape Town got very excited when we partnered for a TEDx xLab and got goodies in no time, I think we could try ask him to go after sponsorship, he seems to be that sort of guy.
The other nice thing of the 'exhibition' discussed in another thread with the public orientated focus is that we can then create much more of a value offering to sponsors - in terms of them being noticed and being able to exhibit themselves. I have learnt some bits on what stuff sponsors want. Here I think we need to invest a bit into a good marketing strategy (both pre- and post-). Max Kaizen and Robyn Farah are a few of many that can help. Social media & possibly television obviously big, here.