Like George, I use water and Vallejo cleaner after spraying their paints. I do also use plain old Windex (not sure if SC Johnson use the same product name globally) as it is a whole lot cheaper than the Vallejo branded stuff and it seems to be the exact same product but with a blue colour.
Keep in mind that I also break down the brush at the end of each session and soak in lots of clean water just to make sure no residual cleaning solution remains. So far so good.
Thanks for all the info guys. I have some Vallejo airbrush cleaner ordered and it should be here Friday so I think I will be going with that and water.