Free Day at the Skirball
All of the Skirball's exhibitions are free to the public on Thursdays (12pm-5pm). The campus grounds and Ruby Gallery are always free, as is parking, and no tickets are required to access the shops or dining areas.
Note that the Noah's Ark portion of the museum, while also free on Thursdays, requires a timed ticket to enter.
Check out other free museum days in LA and OC.