Key DSLR features
Low Light Capability/ISO Speed
If you're likely to want to shoot in low light, whether it's sunset landscapes or cosy jazz clubs, good low light performance is a must. Most DSLRs can shoot at ISO 3200 and some go to ISO 6400, but performance varies a lot between different cameras.
Also known as anti-shake or vibration reduction, this is either built into the lenses (Nikon, Canon, Panasonic) or into the camera itself (sensor-based, e.g. Sony, Pentax, Olympus). Though it's considered that lens-based stabilisation is slightly better, it ties you into buying pricier lenses to get the benefit; sensor-based stabilisation works with any lens.
Burst Mode/Frame Rate
Particularly important for action and wildlife photographers is the ability to fire off a number of images in quick succession. Even the most basic DSLRs now boast a frame rate of 2.5fps but some are much faster. A good buffer memory is important; it's where images are stored before they're saved. The larger this is, the more images you can shoot before it fills and the camera grinds to a (temporary) halt. Raw files, being bigger, fill the buffer quicker than JPEGs.
Every time you change the lens on your DSLR, tiny dust particles can enter the exposed lens mount and land on your sensor, appearing as annoying marks on your pictures. Dust is also created by wear and tear of the moving parts inside the camera. Most manufacturers have a dust removal system that cleans the sensor in one way or another, except Nikon, which argues that it isn't a big issue.
The increasing popularity of shooting home movies or even professional films on DSLR means that the appearance of a high- definition video mode is becoming all the more important. Plenty of DSLRs now offer the function, from the beginner EOS 550D up to the pro end models.
One of the benefits of SLRs is the degree of customisation they allow. Choose which dials control which features, or decide whether you want to shoot JPEG, Raw or both at the same time. Do you want the file numbers to start again when you reload a card or carry on where they left off? Control how your picture looks, too, in your choice of colour space, in-camera sharpening and other parameters.