How many stops can a digital camera capture?
Additionally, does anybody know what the dynamic range is for negative and positive film, the human eye, computer monitor, the television, etc...
The answer will most probably change in time.
Current top cameras are said to capture around 10-11 stops at base ISO, less at higher ISOs, see DPReview tests of Nikon D3X for example. As a sidenote - you won't probably like the pictures that are processed to measure the maximum dynamic range, they'll simply lack contrast you'd expect from "normal" picture.
Negative film is said to have up to 9-10 stops of latitude and reversal film around 5-6 stops. What you're actually able to see also depends on the medium used to present the picture - prints from negatives are usually limited to what the paper can reproduce, slides to what can be projected and digital images to what the monitor is able to show.
Update: I've made a DR test on my 5D (the old one, not mk2) and with default settings I get 9 stops of usable range, with special processing 11+ (and there is probably more room on the shadows' side):
It's not meant to show the theoretical maximum, but rather that 13-14 is not out of this world, if sensor from 2005 can capture 11+ stops.
The exposure latitude, as it referred, is generally about +/- 5 stops for digital cameras (so 10 stops overall). There are techniques, such as HDR, that artificially increase the range.
Traditional film is generally considered to have a slightly wider latitude, and this does very not only on the type of film, but brand, age, etc. Generally it's more forgiving, and you can rescue an over exposed roll by under developing, for example.
The ranges used tend to follow the average human eyesight (which again will have different performance based on age and genetics), which is why photographs appear to be realistic.
There is an easy trick: "measure" for yourself:
take your camera.
Of course the result depends on your jpg settings (contrast etc) in cam, but it is probably more realistic than the marketing numbers from the cam maker.
Now consider this though: that photographers often place certain criteria firmly in mind before shooting or fuming about the lack of dynamic range in the camera they are carrying around. For one, they will jot down the media that will finally display the image.
Newsprint on pressed newspaper pulp without any glossy coating have a hard time showing shades of gray or shades of color.
Highly compressed JPEGs is not often blamed for throwing away absolute levels but will throw away intermediate levels of shades, making photos look digitized and unnatural. But that's outside of discussion here, just mentioned for completeness.
Web visitors are an important demographic of viewers. And widely visited websites often have to consider that the mass majority of the viewership are using LCD screens that are probably somewhat aged and in all likelihood not truly capable of showing 256 shades of RGB. LCDs and plasmas actually capable of representing shades that are near pitch black are often high end home theater components that costs thousands--well out of the reach of the masses.
Even highly regarded fine art giclee photographic paper designed to be used with the highest grade of piezo electric inj-jet printers have limitations. They can be coated with a metal- or pearl- like sheen and it still won't bridge the considerable gap.
So if you want dynamic range, you'll want it because you want to capture both the sun shining through the canopies of a lush central american rainforest but also the dimly lit fern at the forest floor all in the same picture. That's nuts. And not possible. [Actually it's well within the realm of the possible, just not fun. Think lots of ND filters. Think specialized one-time-fire-and-then-dispose flashes that can light up the entire forest--crazy! That's if the mosquitoes don't get to you first.]
And not printable. I don't know, maybe with OLED displays and more fancy technologies we can start getting close. Maybe sparks of electricity suggesting how that image might look like to our brain using a Matrix-like jack-in would work and our brain would be capable of imagining infinite dynamic range. But thanks to the limitation of output devices and output media--you really are safe.
I guess this is a long winded way of saying don't worry, hang loose.
When talking about dynamic range for digital sensors, its best to look at real-world tests. There is a very wide variety of digital sensors on the market these days, ranging from smaller entry-level DSLR sensors to the advanced full-frame sensors in top of the line camera bodies. When reading about a camera, you'll often come across terms like "maximum dynamic range", which for current FF bodies may range up to 13 or 14 stops. Take these values with a grain of salt, however, as real-world performance in common scenarios tends to differ.
The "average" dynamic range is a more useful value. Most of the reviews at dpreview.com include a dynamic range test. These tests include comparisons of the tone curves of real photographs to compute the average real-world dynamic range. Most current digital cameras have probably 6-9 stops of DR, which falls off as you increase ISO. Top of the line camera bodies often provide more even DR throughout their standard ISO range, but tend to rapidly fall off as you use extended higher ISO settings.
The full theoretical maximum dynamic range of a sensor can only be achieved by reducing signal-to-noise ratio to a baseline (usually ISO 100), and by applying a linear tone curve when processing the RAW data. Applying a linear tone curve results in flat, dull, low-contrast images, so most all cameras and software that support RAW apply non-linear tone curves, which effectively reduces the the usable dynamic range. (Think of it like taking a piece of string...pulled strait between two points, the points can be farther apart than if you add a curve to the string between those two points.)
I recommend reading the Nikon D3X and Canon 1D IV DR studies to get an idea of the usable dynamic range these cameras offer. Read the studies carefully, and note that artifacts like noise in higher ISO settings have an effect on the resulting images. They can often reduce the effective usable dynamic range depending on the scenario (i.e. low-light shots often suffer greater degradation from high ISO noise, loosing DR.)