I use http://www.assembla.com/. I've got a workspace for each project and ongoing process (e.g. "Taxes"), each with a wiki to collect notes and links, the ability to write tickets, assign tickets to milestones, send messages to the process, &c. SVN, too, for projects that need that (I don't use version control on my tax files, but I could now :-). So far, this has been a splendid arrangement.