If you use Remember the Milk to manage your to-do list on the web, but you want to see all your tasks in iCal on your Mac when you get home, TaskSync a free OS X app provides two-way syncing between Remember the Milk and iCal, so any changes you make to one task list will soon show up in the other. You can even use the @ symbol in iCal to create a tag that shows up in Remember the Milk.
TaskSync is also smart enough to let you choose which task lists you want to sync, and how often, so you don’t have to worry about cluttering up your iCal with unneeded Remember the Milk lists (or vice-versa). And, as Lifehacker points out, you can always use RTM as a middleman to send your iCal tasks to other services and platforms, including Outlook, iGoogle and RSS feeds.
More Info: TaskSync