What if your checkbook kept track of all your bank and investment accounts, analyzed your spending habits, calculated a budget and made savings suggestions that were actually helpful? Well, then your checkbook would be Mint, a free Web-based service that (with your permission) takes your information from banks, brokerages and credit-card companies and collates it into a single, easy-to-manipulate ledger. Mint is powerful enough to handle all but the most complicated of portfolios yet intuitive and flexible enough to — believe it or not — make home-accounting chores kind of fun.