TS, it really depend on what kind of results. It is better to get the lens to suit the type of photography you want, than to get a lens than try to fit it.
When you say street, do you need to have shallow DOF, with nice bokeh, or are you the type that want to capture the interactions of people with the environment.
If you are into shallow DOF, then a fast zoom ie 24-70L, a 50L or even a 35L. These are not cheap lens, and neither are they light-weight.
If you are the type that likes to capture the latter, you will usually shoot at f4 - f8, with a wider lens ie 20mm, 24mm 35mm and your nift 50mm. in this area, you do not really need a L lens. Stop-down, above mentioned lenses work very well, and they are a lot lighter to carry around. What you may want is to get a flash ie 580exII or a lighter 320ex to provide fill in light. in darker areas.
Hence, look for gears that suit your needs my 2 cents worth.