With Teamlab.com you can create many projects each with milestones and tasks and assign them to team members who are auto emailed on changes, or when someone adds a comment. I find this feature very useful as keeping track in emails can be quite tricky. It can also host a wiki and allow you to store and edit documents on the site. They seem keen to expand on the site too.
My accounts and book keeping is made much simpler thanks to freeagent.com. I use this to track the time I spend on a particular contract and then generate the invoice for it. It also file VAT returns and the PAYE RTI stuff. Very useful time saver.