In SF Bay Area - sperm donation.
I do not personally know any SWEs who do this, but a couple of my friends (and me) who work on their startup ideas do.
Link to an example of how much you will get paid.
Here is the math, assuming you are in great health:
one 15 minute visit => 6+ vial Yield => $175
You cannot do it every day. There should be a 2-5 days abstinence period.
=> best case scenario => 3 times a week.
=> 4 weeks * 3 times per week * $175 per donation = $2100
As you can see in that link, there is a $1000 bonus if you make 12 monthly visits.
=> $3300 per month.
This is good for ethical reasons as well -> you help women with an ultra-important personal problem - how to become a mother.
In a time when the population is aging, you help to mitigate this problem with your own hands.
If everything is so good, what is the catch?
Such programs are picky about who they accept, claiming the acceptance rate is 1%.
I do not know what is the quality of the initial pool of candidates, so hard to tell what percent would be for the pool of SWEs that need side income.
P.S. I am quite serious about all of it, as I am part of this program as well, and the link with how much you get paid is for November in the company that I am donating to.
P.P.S. I wish I had known about such an option when I was a graduate student making $1600 / month for teaching. An extra $3k would make a huge difference in the quality of living and how much I could send home.