Holiday is coming and you might want to look for some great lenses for event photography. Beside these lenses, you might want to get a flash (Canon speedlite) as well and learn how to use it well to get the perfect images.
Best lens for Canon APS-C size camera: Canon Rebels plus 40D, 50D, 7D
Canon EF-S 17-55mm f/2.8 IS USM Price: $1000
This lens is almost perfect for event because it is wide enough to cover the entire floor, and it is long enough to get a nice portrait. It also has constant f/2.8 aperture and Image Stabilization which is very useful in challenging light situation. My only rant is the lens built-quality is not great and no weather-seal either.
Canon EF-S 15-85mm f/3.5-5.6 IS USM Price: $750
This new lens (2009) is alternative to 17-55mm, it is even wider and longer, but the aperture is quite slow (1-2 stops slower) so, it is better for outdoor events rather than indoor. For indoor event, you will definitely need to use flash with this lens. Another good side is the lens is cheaper.
Best lenses for 1D series camera (1.3x factor)
Canon EF 16-35mm f/2.8 USM $1420
When mounted in 1d mark series camera, the focal length will be around 20-45mm. This is a great wide zoom range for event photography or photojournalists. It covers massive amount of field of view. But it does not reach very far. Therefore you might need another lens such as…
Canon EF 85mm f/1.8 USM Price: $380
This prime lens are best of the buck Canon lens. The image rendered is very contrasty and the blur is smooth. The Auto focus speed is good and snappy too.
Best lens for full frame cameras
Canon EF 24-70mm f/2.8 L USM Price: $1300
This is a very popular pro-quality lens but it is best when mounted in full frame camera. Image quality is excellent and great for any type of photography including portraiture. Unfortunately, it does not have image stabilization.
24-105mm f/4 IS L USM Price: $1150
This is also a very popular general purpose lens. It is long enough for close up portrait, and wide enough (in full frame camera) for indoor. It has image stabilization but the aperture is fixed at f/4 which is not that fast. You might want to invest on flash too.