I'm using the lib_mysqludf_preg library for this and a regex like this:
SELECT PREG_REPLACE('#<[^>]+>#',' ',cell) FROM table;
Also did it like this for rows which with encoded html entities:
SELECT PREG_REPLACE('#<.+?>#',' ',cell) FROM table;
There are probably cases where these might fail but I haven't encountered any and they're reasonably fast.