As far as I can tell, the only VFR Corridor (see AIM 3-5-5(b)) that exists is in San Diego. Is that correct or are there others elsewhere in the US?
San Diego is the only location that has a "VFR Corridor" that I can find. There may be others, but I've looked at many of the main Class B airspace areas (San Francisco, Las Vegas, Los Angeles, Phoenix) and they do not have "VFR Corridors." It is likely that there used to be more "VFR Corridors," but have since become SFAR airspace (see 14 CFR Part 93) for more information.
Also, if you do a word search in FAA JO Order 7400.11F, Airspace Designations and Reporting Points, which provides a list and the dimensions of all Class B Airspace areas, you will find that the only Class B showing a "VFR Corridor" is within the San Diego Class B (see page B-61, Area L).
Operation within "VFR Corridors" like in San Diego do not require communication with, or authorization from, ATC.
Los Angeles, for example, has several "VFR Transition Routes" all of which require an ATC clearance. However, Los Angeles also has a "Special Flight Rules Area" (SFRA) route that, if flown as required using the rules shown on the chart, does not require ATC authorization (conducted in accordance with FAR 93.95).
Some Class B airspace areas have "VFR Flyways" (avoiding, but near, Class B airspace) and do not require an ATC clearance.
So, of course, review the Terminal Area Chart for the area in which you plan to fly near, in or over Class B airspace for the specific rules that may apply to you.
Here is a link to Section 5. Other Airspace Areas in the Aeronautical Information Manual. See specifically paragraph 3-5-5, "Published VFR Routes" that provides additional pertinent information.