Google desktop has this neat "widget" that is a stop and start timer that you can use for timing some of your daily activities:
http://desktop.google.com/plugins/i/limiter.html?hl=en
Also, for billing, there's this nice online billing tool called
FreshBooks that can help you bill clients an hourly rate and keep track of accounting stuff.
I use it for billing web design/web hosting clients and it's pretty nice.