CNN recently looked at four  absolutely free online personal finance management webapps and came away with a winner. They took a look at the accounts the tool tracked, how easy it was to use, what they liked best, what they liked the least, and the bottom line of each of the four tools. From what I know about each service, I can’t say I disagree with their assessments of each tool.
Mint.com  was named winner, edging out Yodlee’s MoneyCenter, because of their recent investment tracking additions. You can now track bank accounts, credit cards, loans, and investments. Yodlee can track a couple other things like frequent flyer miles but it can’t track investments; I think investments trump mileage anyway, especially since I fly Southwest.
Another notable plus for Mint was it’s “inviting layout” (I considered Mint to be the most visually attractive of all the tools when I reviewed Mint ) and their biggest minus was the thinly veiled advertising. I don’t think you can blame them, they have to pay the bills somehow.
#2 Yodlee MoneyCenter
As mentioned earlier, Yodlee MoneyCenter came in second with the most comprehensive feature-set but was austere in its layout. Another knock against Yodlee was how difficult it was to navigate. Yodlee is the backend that powers many of the other personal finance tools. Mint used to (and may still use) it to retrieving account transaction data.
#3 Quicken Online
Quicken Online  has been around for a while but only recently offered their online application for free. They too can track bank accounts, credit cards, investments and loans (the same as Mint.com) and have been in the business for many many years, which means strong customer support. The only downside is you can’t sync the online with the desktop app.
Wesabe has since closed its doors and been replaced with its own forums.
Wesabe  took fourth because it had a much shallower feature-set letting you only get data from bank accounts and credit cards. Until recently, Mint.com had the same feature set as well but they’ve now put some distance between them. One security plus with Wesabe is that you retain your account login credentials on your computer, rather than storing them on the app’s server (encrypted, of course).
Of the four, I’ve used Quicken Online and Mint.com and, if forced to choose one, would pick Mint.com because of its interface and rich feature-set.