I have high hopes for OmniFocus when it comes out, but those desperate for something as good as KGTD, even a little better, that works now might wish to try
iGTD. As of the latest release it is the first real alternative to KGTD I've seen for Mac OS X. It is a solid and well thought out program which includes iApp integration and a QuickSilver plugin, and all the GTD goodness you'd want. I can easily imagine how something like OmniFocus could be even better (especially on the GUI front), but at least there is no need to wait indefinitely to start getting things done.