On the All Sites page of SE there is no way to search for a community by its name or description. The only way to find a community is to read each site individually as requested by the description of the site-recommendation tag here on MSE (or use Ctrl+F, but I think for the case of usability we can ignore that). I believe it could be causing some MSE site-recommendation questions and off-topic questions on other communities to be posted unnecessarily.
The All Sites page is made easier to look through with the category filtering, but the lists remain long and the categories arguably overlap somewhat.
The drop-down in the top right of the site has such a feature (shown below), but I believe it would be even more useful if it was also added to the page dedicated to showing off all of the communities. Not everyone is going to know to click the SE icon and scroll down to find the search area.