Budget Envelopes by Mobile Innovations LLC
Budget Envelopes is the first app that I have noticed that really helps to keep things in my life simple.
This way I can sync the budget and expenses with my wife. We can keep track of our spending and budget ourselves easily with this app.
When living paycheck to paycheck, this is one of the best apps to use. Sometimes the glitches are annoying, but it works most of the time. :)
Just FYI, if your are not on a paycheck to paycheck budget anymore you can use Mint. Mint really helps putting all of our accounts and credit cards in one place and helps create a budget.