Getting married is, without a doubt, by far the best financial decision I've ever made. I doubled my income and only very marginally increased my living expenses. I'm saving more money now that I ever thought would be possible, and that savings generates income in itself as capital gains and dividends which is reinvested and compounded. It's friggin amazing! After several years of marriage our passive income (dividends and capital gains) has become significant.

That being said, I wouldn't advise doing it solely for financial reasons. :)