When photographers take pictures at events, like at the latest British open golf tournament, you can hear a lot of loud shutter(?) noises? Is that really necessary for a digital camera? Especially when photographing wildlife, it is important to be as silent as possible. What kind of camera can be used for this?
True DSLRs will always make noise by moving the mirror. This can be reduced by using mirror lock-up or in some modes of live view, but if you need to be really quiet you have to use either something mirrorless (like Panasonic GF1) or a Sound Blimp, which is basically a soundproof box around a DSLR (see video from John Harrington).
I believe the most silent DSLR is the Pentax K-7. It is quiet due to both dampening and weathersealing.
K-7 vs A900 for reference http://youtube.com/watch?v=6SzFL1FoheM
See this question: Why don't they make all DSLRs with an electronic shutter? - there are significant costs, in terms of camera performance, to using electronic instead of mechanical shutters.
You can usually make DSLRs a bit quieter by using the mirror lock-up and/or "live view" feature, if that helps...
Ken Rockwell claims, and I agree, that the D5000 in quiet mode is pretty darn quiet. I haven't measured mine, but it is pretty hard to hear from across the room in quiet mode. That being said, I don't like the delay, and only turn it on when I really have to.
Answering the original question, yes there are. At the moment here are your options:
A) Timing the loud shutter to make its obnoxious sound before snapping the shot silently in the golden silent moment. This is possible with many of the current DSLRs supporting Live View.
B) Using the latest mechanical mirror-flip technology which slows down the flip up to reduce noise (the mirror flip up is pretty much the loudest contributor to the noise you hear upon shutter release). Both Canon and Nikon are pretty much committed to using this new technology in newer DSLRs, as other answer entries have mentioned D5000 is well known for having this feature.
C) There are enclosures that completely wraps around the entire DSLR + lens and muffles the sound. It's added cost but may just allow you to use a camera in places where it's taboo, like concert halls.
D) Use an camera that uses alternative shutter mechanisms. Cloth and leaf shutter comes to mind.
E) Use compacts. Compacts tend to have a very small sensors--even premium compacts have tiny sensors. And as a result the shutter is either completely substituted with an electronic shutter or the shutter makes very little sound. And these compacts have no mirrors to flip either--which pretty much contributes the most noise in high performance DSLRs.
F) A special mention can be made for premium compacts and mirror less cameras with electronic viewfinders like that of the Olympus/Panasonic micro four-thirds system or the Samsung NX system and last but not least the Sony NEX platform. As you know the lack of mirror flipping means a great deal of noise can be dampened.
Keep in mind other sources of noise, if you are wary of noisy cameras because you need to record sound, forget about it. You almost always need to have someone carry a dedicated boom with the mic attached because other things on your camera will make a ton of noise. Here's a short list: 1) working with the tripod and ballhead; 2) the rustling of sound made by your fingers operating the camera; 3) the image stablization mechanism inside the camera body or inside the lens will also contribute noise; 4) working with the focus and zoom rings will also make some grinding noise with lense not in the best condition; 5) the auto-focus motor, even the silent type, can make an audible noise that will be recorded by any sensitive on-camera mic. This is just a short list--there's more. But it's kinda drifting off topic.
The expensive solution : Leica M9 is very silent.
Dslr have mirrors that needs to be flipped up when taking the photo so they tend to be on the loud side. You've locked yourself out of quite some options by using the term dslr in the question. Outside dslrs, you have: Leaf shutter cameras are very quiet. But the shutter would be inside the lens, not the camera, so the lens is usually not interchangable. Example: fuji x-100. Sony has something which looks like a dslr but with a translucent prism instead of a mirror, so should do less noise. Mirrorless cameras have no mirror (duh) but still a curtain shutter, as dslrs do, which in itself can be pretty loud. Some have a "electronic first curtain" which helps. Olympus high range mirrorless (e-m 5 or e-m 1 i guess) supposedly have a very mufled and faint shutter noise. Any of these cameras can have a 100% electronic shutter mode. Many cheaper cameras (such as the one on the iphone) only have that. An electronic shutter is totally silent but will produce ugly rolling shutter "jello" effect with movement and banding with artificial lighting. In the future, global electronic shutter or very fast sensor readout times should solve the rolling shutter problem and make noisy mechanical shutters obsolete. These features are already available on very high end (read: totally unaffordable) professional video capture devices.
To answer just the final part of the question, I'll second the Pentax K-7 - it's probably the quietest SLR I've used (and it's not a mode, the shutter is just generally quiet). There are videos on YouTube which demonstrate how quiet.