Serious Eats - seriouseats.com

I've tried the once-a-week thing but am far too impatient to maintain my sanity in between weighings. What works for me is a daily morning weighing right after rising. Like randomeater, my numbers go into a spreadsheet from which a trend is monitored. Since your weight can vary so much from day to day, monitoring the trend really is key.

Without getting too deep technically, a good way to track the trend is to use what the propellerheads call an "exponentially-smoothed weighted average." Really, all you have to do is add 90% of the previous day's moving average to 10% of the latest weight to get today's trend value. Even if your weight goes up and down from day to day, as long as your daily weight readings stay below the moving average, your diet is working.

John Walker goes into far deeper detail on his Hacker's Diet web page. Despite the name, THD isn't really a diet but a good explanation of the basics behind losing weight and it's worth taking a look at. Good Luck!