Well there's always Calorie Count which seems to be the most highly rated one, and is maintained by About (considered highly reputable). This is the one I use, so just from experience here are some pros and cons.

Pros:

Cons:

Here's why you don't trust the numbers on the cardio machines!

These two pics are calorie meters from the exact same workout. The first (54 minutes, 733 calories) is from the elliptical machine itself, even after setting it with my age and weight. The second (54 minutes, 484 calories) is from my heart rate monitor and is closest to accurate.

The machines have no idea how hard you are or aren't working. It doesn't account for your experience, health, or fitness level. Usually it won't even ask for your weight or age. 120lb teenage girl doing the elliptical for an hour on resistance level 1 and apparently she burned 800 calories without breaking a sweat? MY ASS.

If calories are your focus, get a heart rate monitor. How fast your heart is beating is the best indicator of how hard your muscles are working, and that will give you the most accurate numbers.

(Or better yet, don't even think about calories when you exercise and instead train until you are finished!)

I’ve read through The New Rules of Lifting for Women probably five times now and this quote still makes me want to stand up and clap wildly.

"Calorie."

It’s become a tiresome word; a word that a shallow culture has given unnecessary weight and inaccurate connotations.

The diet-industry concept of “calories” turns food into scary numbers and twists biological science into ridiculous fads.

Everything has “only 100 calories!” or “1/3 fewer calories!” or “all the flavor, zero calories!” with hardly a mention of other nutritional merit.

I venture into “health” sites and become more jaded every day to see how many people obsess over Counting Calories, with a capital C; stripping away their intakes to some arbitrary magic number, never mind health or a balanced diet.

I am hereby stripping the word “calorie” of its undeserved power and stigma.

A “calorie” is not synonymous with a fat cell; it is a unit of energy available in food to be either used in the building of new tissue, operating vital functions, burned in the digestive process, or stored as spare fuel.

Calories do not make you fat; poor body management and faulty food math make you fat.

The number of calories at the end of your day matters so much less than their quality.

I am not willing to live a lifestyle reliant upon numbers, and the Calorie Police can kindly shove it.

Here’s an analogy for all you low-cal eaters and starvation dieters.

Ready?

Imagine the U.S. economy right now. It’s pretty bad, right? Jobs are few and far between. Once-steady incomes are at risk. People are being particularly frugal because they’re concerned about their cash flow. And that’s how it goes. When the economy’s good, people spend freely and easily. When it’s bad, people cling to their dollars with miserly little fingers.

A human body acts the same way. Calories are your body’s dollars, to be spent and used and stored the way your body sees fit. Keep the calorie supply flowing properly and your body will happily “spend” spare fat like there’s no tomorrow… but cut off that calorie supply, and your body holds on to that fat like grim death.

The choice is yours.

As always, my inbox is open if you have any questions.