How can I share my availability with a client who uses Outlook?

I have a favourite client, on Outlook, who often needs to schedule appointments including both me and third parties. It makes their life a lot easier if they can see my availability while talking to the third party, but I have really struggled to find a way to make this possible. For a while Tungle.com worked brilliantly, but then RIM bought it and broke it - so now we're back to them having to call or email me every time, which is tedious for everyone involved. I have tried sharing direct from iCal but it doesn't always work 100% and besides I don't want to share details - only free/busy information. Has anyone cracked this? I can't believe such a basic piece of functionality is missing...