I started banking with Simple (an online bank) back in November, just around the time I started reading MMM, and I have really enjoyed it. One of the features I like is that it seems to be better at anticipating expenses than other online banking apps. It accounts for monthly recurring payments and subtracts them from my available balance well before the deduction actually takes place. It also automatically takes away $25 from your balance whenever you buy gas, until the actual purchase amount is verified.
What I like best about Simple is your ability to set "goals" which act like little partitions within your account. You specify the amount and the timeframe, but you can always pause the goal or transfer more money into it to speed it up. You can also choose to "spend from goal" which is how I handle monthly rent. I don't keep money in these goals for long (either use them for rent or transfer the amount into my emergency fund or IRA), but I love them because they create an artificial environment of scarcity, which causes me to automatically reduce my spending. I have around 70 dollars a day that automatically gets moved into various "goals" so that my available balance is constantly shrinking even though I'm not spending. Just seeing that low number, even though I know I have money in the goals, really makes me second guess any non-necessary purchases. I've saved about 3000 dollars this way since November.
Any other Mustachian Simple users out there?