The question says it all. I am looking for a chart or a table that displays the sweetspots for various Canon lenses. Is there anything available online?
You can use a database, such as DxO Mark, to get close. The database contains every currently available lens in the Canon EOS system as well as several that are no longer available. Here is a link to the EF 50mm f/1.8 II lens. Click on the 'Measurements' tab, then 'Sharpness' on the line below, 'field maps' and/or 'profiles', and finally a specific aperture to see the tested results. Note that in general only whole stops are tested, plus the lens' maximum aperture wherever it may fall. The 'global maps" can also be helpful with zoom lenses. You can even compare the same lens' performance when tested on different bodies.
The tip of @Michael Clark it's very good, DxO Mark it's one of the best websites to indentify the 'sweet sopt' of the lens. But I really like the Photozone and it shows the most sharp image that you can get on the lens, for example, the 50mm f/1.8 II. In this image you get a MTF score according to your aperture, which is easier than analyze the graphic. I didn't find a table of all lenses (just with graphics, which is not so good).