iOS-only: If budgeting your money has never been a strong suit of yours, perhaps in part due to the complicated and somewhat time-consuming task it can be, you may want to take a look at Left to Spend—an iOS app that gives you the cold hard truth of what's left (and absolutely nothing else).
If you're not a fan of minimalist apps, you're probably going to hate Left to Spend. All it does is let you enter the amount you can spend per day (and it guides you on how to find this number) and keeps track of what you spend on a daily basis. Every time you look at the app you're confronted with the image you see above: this is all you've got left, buddy. Its dark and ominous type reminds me of the (incredible) Xbox 360 Arcade game Limbo, so I'm convinced that if you need an easy-to-use app that will scare you in to sticking to your budget you can count on Left to Spend. It'll cost you $1.19, but if it can help you stay on top of your budget it's worth it.