Most corporations are leechers, they just take open source stuff as a way to save costs, without returning anything back.

I have seen this happen in many Fortune 500 projects.

The 'Donors' page on the FreeBSD Foundation website shows both corporate and individual sponsors (and roughly, the amount donated):

http://www.freebsdfoundation.org/donate/sponsors.shtml

Sadly, the number of corporate ($$$) donors has dropped off in the last couple of years...

Netflix is conspicuously absent, for one.

https://signup.netflix.com/openconnect/software

I see Google on the list of corporate sponsors. Do any Google services use FreeBSD?

Given how large Google is I'm certain they use FreeBSD in some form somewhere. Still it's kind of fun seeing Google who is predominantly Linux-based as a major sponsor and not Apple which likely ship code from the FreeBSD project in every device they sell. Also nice seeing Juniper contributing back but I can't see anything from Cisco...

A number of donations typically come in late in the year - it's really not possible to draw year-over-year conclusions until the year's over.