Check out www.getmytime.com Pretty nice tool/service for time
tracking via the web, and it exports into QuickBooks, which is
just the ticket for invoicing and accounting in general.

There is a tool that comes (or came) with QuickBooks called
'quick books timer' which runs on your desk-top. It's a piece
of junk, crashes the computer and itself from time to time and
is generally a pain in the butt.