Ever since DynDNS stopped to offer free accounts, I used FreeDNS to dynamically update two hostnames. However, FreeDNS offers wildcard DNS records only for premium members and while I could spend $5 per month for their service, I wanted to find out if there are other, free dynamic DNS providers out there.

Believe it or not, DMOZ is still online and has a list of Dynamic DNS Service Providers and one has to click through every item to find out about the features of each provider. Keywords: free¹⁾, wildcard DNS, OS agnostic update process (ideally a simple update URL via TLS/SSL).

There's the Best Free Dynamic DNS Services list that got updated in 2014 evaluating quite a few providers and I used this list (and the DMOZ list) to narrow down my provider of choice. In alphabetical order:

ChangeIP offers free dynamic DNS but did not offer wildcard support, IIRC.
Apparently CloudFlare is offering (free) dynamic DNS as well - but no, thanks :-\
DNSdynamic offers a simple API to update IP addresses, but no word on wildcard DNS support.
DNSExit supposedly offers wildcard DNS, I haven't signed up yet to find out if this applies to their dynamic DNS offers too. They also offer a dynamic DNS update URL, which is neat.
DtDNS does much more than dynamic DNS and has all the goods too: wildcard DNS lots of update clients to choose from.
DuckDNS looks like a worthy contender: free, wildcard DNS, excellent documentation on how to do IP address updates. And a nice duck, too! :-)
duiaDNS offers a free package for personal use, with IPv6 address updates and two sub-subdomains (e.g. {foo,bar}.bollocks.duia.us under bollocks.duia.us). So, not really a wildcard but sufficient for my needs. Also, while they offer update clients for a fair share of operating systems, one can use a shell script to issue IP address updates.
Dynu offers wildcard DNS but I couldn't make out if they support an easy update URL for the IP address updates.
hopper.pw looks promising too, it's free as in beer and in speech, use an update URL for IP address updates but I could not find any information if they support DNS wildcards.
Hurricane Electric is a real beast, they offer much more than dynamic DNS and really seem to know what they're doing. However, they only seem to support dynamic DNS for your own domain name but don't seem to offer any own placeholder domain names. Too bad, really - but then again HE is not for n00bs who don't have a domain name to spare for their dynamic DNS setup :-)
I even tried no-ip once, but one has to update the hostname every 30 days (or they expire) and they charge for wildcard support, although I don't know if they even know what wildcard DNS is - their "purchase a wild card" link points to purchasing a wildcard certificate.
System NS offers free dynamic DNS during their beta phase. But they're beta since 2013 and nobody knows what happens when the beta phase ends. IP address updates are done via an update URL (but their certificate is expired since 2014).
YDNS looks nice, has IPv6 support too, a simple update URL (and an update client) but there's no wildcard support.
Zonomi offers free dynamic DNS, and wildcard DNS too, but I don't know if this applies to their free offer as well. Also, their webserver doesn't really support SSL.

I'll take a closer look at the bold entries in the next days and will report back with the winner :-)

¹⁾ why free? No reason, really. I just wanted to see what's out there and if the service is good I intend to donate, but I don't like to have a contract for a service like this, that's all.