Bookmarks

Since I am having to work on multiple operating systems and multiple machines on a regular basis, I face this problem on trying to keep my bookmarks in-sync. I just wonder if there is any tool that I could use to maintain my bookmarks over the internet and that I could download on to the browser everytime I log on. Something like that (along the lines of, say, bloglines) would be very useful. Irrespective of which machine I am using, I could just log on to my "bookmark account" on the net and get my latest bookmark list.

Does anyone know of any similar stuff that already exists?