My most common lens of choice is a a Canon 16-35mm 2.8 L series. This lens is remarkably sharp across all aperture settings and provides me with a great deal of flexibility when shooting wide and up close. Mounted to the front of a camera with a 1.6 multiplication factor, At it’s longest setting 35mm it appears very close to what the human eye sees and therefore provides nice everyday shots. However when mounted to a full-frame dSLR it can achieve very wide shots.
NOTE: Most digital cameras have a sensor that is smaller than the surface of 35mm film. So the size labeled on the side of a lens is not accurate. If your camera’s sensor is smaller as previously stated you will need to calculate the focal length using your camera’s focal length multiplier (FLM). In the case of my camera, the Canon 20D, I have a FLM of 1.6, in this case 35mm x 1.6 = 56mm. But in the case of my Canon 5D Mark II this lens needs a brother and sister, hens the reason for my 50mm 1.4 and 70-200mm 2.8 L Series
When buying your lens it is important to note this distinction. The down side of FLM is that you have to buy even wider angle lenses to achieve wide angle shots. The upside is that you gain length with less, in other words 200mm lens on this type of camera is actually 320mm (200mm x 1.6 = 320mm).
It can be said, the lens makes the camera versus the other way around. My suggestion is look for used equipment if you can’t afford to buy new, but don’t sacrifice quality. I’d hate to see you spend $500 on a lens of poor quality when a used lens could have out perform and only cost you a couple of hundred dollars more.