After seeing Tina Louise there, I went to IMDB to check out where some of the other actors were. Most of them are dead, in fact. But Dawn Wells (Mary Ann) is still going strong! She's performed in over 100 theater productions in her lifetime and still doing them. That's a lot!
Here's an interesting blurb from her bio on IMDB:
It has long been stated that the entire cast of Gilligan's Island never received residuals beyond the first four reruns of each episode. This was true for the entire cast except Dawn Wells. When the show was picked up by CBS and Dawn was cast to replace Nancy McCarthy, she was married to her agent at the time. In her original contract she was to be paid $1200 per week plus the residual contract the 6 other castaways received. Her husband/agent said that should the show become successful Dawn would not benefit from receiving such a limited residual option. Believing the show would flop, the CBS executives humored Dawn and her husband and put a clause in her contract giving her long-term residuals should the show ever syndicate. As a result from that clause Dawn has made literally millions of dollars as the years have gone by from syndication of Gilligan's Island. This was never public knowledge. Dawn and series creator Sherwood Schwartz are the only individuals to profit long-term from the series.