Not too long ago I searched through several accounting / money managing software and GnuCash was the best open source software program I could find for the job. To start, I really like it because it works on several different OS such as Windows, Linux, BSD, and MacOS X.
At first the program is a bit complicated to get used to because it uses the double-entry accounting principle where you always have to list where the money is coming from and going to. But, this system was very useful for me to track my money with quite a bit of details of where everything was going to.
With it you can get very useful reports and graphs to have a quick overview of your finances, compared to previews months, to other accounts you set, or even to different expenses categories.
Another thing I like about GnuCash is that it works easily with multiple currencies, just set the conversion rate and when everything is factored together, the currencies are automatically adjusted.
GnuCash also plays well with some proprietary softwares by importing QIF and OFX files. There are a bunch of other very useful features you can see on their website.