Valve are giving away Portal free until the 25th, and there's now a Mac version as well as the PC one
Yet another thing to slow down my writing...
later or possibly not - doesn't seem to want to work. Asked me to update my video driver, but even after I did it says that I need an updated driver, and stops after loading the Valve ID screen. This PC is fairly elderly but seems to exceed the minimum specs, not sure why it won't run. My other one doesn't have enough RAM, so I suspect that is it for now.