I just ran across this interesting source of information on the physiological mechanisms of how the human body processes & burns calories. It's well balanced in its approach, continually emphasizes the basics rather than the fads (”Burn more than you intake” - crazy, I know), and also goes into more detail on the muscle mass vs fat issue that a lot of diets gloss over with a few vague sentences like “make sure to work out so that you don't lose muscle.” Overall it covers much more of the 'why' than many other weight loss resources. One interesting tip:
In order to mobilize fat, a "triglyceride" has to be broken down into fatty acids, bound to proteins, and other time-consuming feats. The good news, is that lipid (fat) metabolism is the main way that your glycogen stores are replenished after exercise. That's why it can be useful to work out in the morning on an empty stomach and wait about an hour after your workout before eating - your glycogen stores are more depleted by the end of your workout and you burn more fat afterward.
Another thing I have experienced myself but never understood what it was:
In general, you'll maximize your fat loss if you wait about an hour after your workouts before eating. The exception, in my view, is when you smell ammonia. Ammonia is essentially nitrogen, and that sensation after a workout is a signal that you've raised your cortisol levels enough to trigger the breakdown of amino acids by the liver (gluconeogenesis). When the body needs energy, it metabolizes glycogen, then fat, then protein. If one isn't fast enough, it goes down the list. But if it's going to feed on protein, you want it to go after something other than muscle tissue. So if you smell ammonia, you should have a protein and carbohydrate containing supplement immediately after your workout, preferably along with a protein stimulating supplement such as L-Leucine (whey protein is about 20-25% Leucine).
It also includes a calculator for your base metabolic rate.
Another useful source of weight loss information (and associated tools) is the Hacker's Diet, which takes a geek's approach to weight loss, combining good tips (weigh yourself at the same time every day, but don't take the current day's weight on the scale as having any meaning - take the average of the last 10 days) with tools (you can't be expected to perform the average in your head, can you? You need a web-based graphing system!).