Mint is an online personal finance tool, and the most helpful and easy to use budgeting tool I've ever used. Simply enter in your user-names and passwords to the accounts you want it to track, and then Mint will automatically download your transactions and assign them to budgets. It also does a great job tracking investments. Mint is complete with an iphone app, so you can check your budget on the go.
I still find that I need to check in on Mint about once a week to make sure it got my transactions right, but this is still really great because it alerts me when unusual spending occurs, and occasionally I find mistakes that I can quickly correct. Usually, Mint has everything right already, so its just a check in the box "yup, everything's good to go" and a quick look to see how my budget is doing. (Speaking of... Looks like I've once again spent too much on my gear budget...
The biggest hesitation i've heard people use against mint is: Is it Secure? The answer is yes. Mint is just as secure as any other online banking site... and even if someone were to get your password, they would have access to less personal information than if they got your password to a banking site. So in a way, its safer than just using online banking!
Obviously, it's important to take standard security measures. Be wary of software on your computer and unsecured WiFi, but Mint is a great tool, and one i use all the time!
Do you use mint? What do you find most helpful about it?