Usability 
Yodlee Money Center is a web based personal finance application. The service, which is free for personal use, is actually an "account aggregator" meaning it lets you view and manage multiple bank and brokerage, credit card, loan and PayPal accounts within a single application. Yodlee can import transactions from hundreds of institutions and when your transactions it automatically assigns each to a category like income, expenses, entertainment, utilities. You can override these categories and setup your own.
Yodlee has Bill Pay too. You can pay bills online from any of your linked credit card accounts and Yodlee can also act as a front end to many bank's bill payment systems.
Budgeting is another Yodlee feature. You set of goals for certain classes of expenditures like entertainment and Yodlee will alert you when get near or exceed your goal. There are budget reports and graphs to help you visualize where all that money went.
Yodlee is the most powerful and feature rich free online money management system I've seen yet. It's not limited to just financial services either. Yodlee can also import and display your gMail, Hotmail or Yahoo Mail, although it just shows a read only view of the subjects of recent mails. To read the full email and reply Yodlee offers a link that automatically logs you into the webmail providers site.
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