We're expecting new software, but that's easy for Apple to keep under wraps as it doesn't really have to be used outside Cupertino, unlike manufactured products like an iPhone. Nothing abnormally secret there.
We're expecting new MacBooks, but the rumour is a move to Haswell, which would only be a spec bump, no new major design, and we have had new model numbers leaked. Nothing abnormally secret again.
There might be a new Mac Pro, but this is supposedly being manufactured in the US meaning there is less of a supply chain to leak from, and my guess is that it's not in manufacturing yet anyway and if one is announced it will be a little way off (it was slated for 'later in 2013').
If there is an entirely new product (probably something TV related) then that would be a big secret that was well kept. But I'm not putting money on that happening. I'm not sure Apple has been any better at keeping secrets than recent years at all.