Concerts at arenas or stadiums are often among the best lit, but due to the stages being larger, and restrictions for where you can shoot from being the norm, these kinds of gigs often have the greatest requirement for specialised equipment.
Many arena concerts require accredited photographers to shoot from the sound desk, the aisles, or even the back of the room. If you're lucky, you may be escorted to the pit at the front to take photos, but this often isn't the case.
If you are a beginner, and you're lucky enough to have gained accreditation for a show at an arena, and you haven't the means to buy fancy professional lenses, an image stabilised 70-300mm zoom lens coupled with an entry-level DSLR body, such as the Canon EOS 1100D, Nikon D3100, or Pentax K-r, should give you a reasonable chance of getting some decent images.
The image stabilisation should enable slightly slower shutter speeds to be used. Even though lighting at arena shows is generally quite bright, this may still be necessary due to the slow f/5.6 maximum aperture of these lenses.
If you're lucky enough to own a camera with in-body stabilisation, then it isn't be necessary to buy a stabilised lens.
Intermediate photographers should be served well by a mid-range camera body such as the Canon EOS 60D, Canon 7D, Nikon D90, Nikon D7000, Sony A580 or Pentax K-7. The direct nature of the controls will enable you to adapt to changing lighting conditions more quickly than would be possible with an entry-level DSLR.
A telephoto zoom lens covering the 70-200mm range with a bright maximum aperture of f/2.8 will be the most useful lens for this kind of concert, although some may find a standard f/2.8 zoom handy for wider shots of the venue or stage.
Most professionals will use a full-frame camera body such as the Canon EOS 5D Mk II, Canon EOS 5D Mk III or (soon) Canon EOS 1DX, or the Nikon D700, Nikon D3s, or Nikon D4 with a 70-200mm f/2.8 images stabilised lens as a basis for a gig kit.
For those gigs where restrictions require images to be taken from the sound desk or aisles, a 300mm f/2.8 prime, or a teleconverter for use with the 70-200mm f/2.8, is necessary to enable close cropped images of the performer. Some photographers may even hire longer lenses up to 400mm or even 500mm for shooting concerts with these restrictions.
These lenses will generally require a sturdy monopod to enable sharp images to be taken. A standard 24-70mm f/2.8 lens will also be required for shooting wider shots of the venue, or for shooting from the pit.