Consultant here...
We used StatSeeker at a large state government WAN (my last gig before
turning consultant) and I personally loved it for graphs and to point
customers to (you can easily set up user accounts where they can log in via
a web portal and they can see the graphs you assign them). I have no idea
how much it costs or how easy / difficult the backend server set up is.
From a network admin point of view, if all you need is graphs you cannot
beat the ease of StatSeeker. I have nothing bad to say about them - their
support is great (but they are on Australian time). It's been a couple
years since I've used it though.
We also had OpenNMS and Intermapper, both of which were kind of quirky, but
seemed to get the job done. We had internal support for OpenNMS, which was
decent (as good as your staff is). Intermapper support was horrible.
Today we deploy a lot of Cacti and it seems to work well, once it's working.
I see a lot of MRTG at our customer sites too. I've seen a few SolarWinds
instances as well. Customers that use these seem happy with their choice.
Zenoss I've only seen at CiscoLive, but I was impressed. Observium also
looks like a good product, but I've never seen it on a network.
-bb
"Vendor" here (technologist role, occasionally helping with sales, at
OpenNMS.com)...
We used StatSeeker at a large state government WAN (my last gig
before turning consultant) and I personally loved it for graphs and
to point customers to (you can easily set up user accounts where they
can log in via a web portal and they can see the graphs you assign
them). I have no idea how much it costs or how easy / difficult the
backend server set up is.
We're in the middle of a project with a customer to replace StatSeeker
with OpenNMS. That's a very realistic goal now that Cassandra is an
option for our time-series metric storage.
StatSeeker can definitely get expensive, but I can't speak to ease of
setup or operation.
We also had OpenNMS and Intermapper, both of which were kind of
quirky, but seemed to get the job done.
Glad to hear we got the job done. I'm the first to admit that custom
graph configuration in OpenNMS itself is still pretty crap (it amounts
to editing RRDTool graph definitions).
That's a big part of why we now have a Grafana data source plugin:
We had internal support for OpenNMS, which was decent (as good as
your staff is).
I'm the person responsible for making the support experience far above
"decent". I'd love to hear your thoughts on how we can improve; please
contact me off-list if you have the time and inclination.
-jeff
+1 for Statseeker. Ease of use etc (price depends on eg site size etc). Can do lots on just one mid server unlike some other bloaty solutions out there. But we also still use MRTG for some local bespoke measurements
PS you can get a free Eval of statseeker. Obnote, don't work for them just a fairly happy customer
alan
+1 for Cacti.
I tried zenoss & observium but still Cacti is more cool in terms of
tweaking templates as well as the tree mode for easy quick representation.
Thanks for starting this cool thread. Will help in getting links to some of
other cool projects which we don't hear around.
Look into AKiPS.. Some of the guys from Statseeker made it better 
May want to check out AKiPS. It's non-free, but we've been using it for
a while now, and it works pretty well. The UI is a little rough, but the
poller is fast, and the graphs render quickly.
https://www.akips.com/
On 2016-03-24, Anurag Bhatia <me@anuragbhatia.com> sent:
"AKIPS continues to lead the market as the only network monitoring system to monitor SNMP, Ping, Syslog, Traps and Netflow, all at one low subscription price, independent of the size of your network “
At $5K/year subscription starting price, I think my definition of “low” differs from AKiPS
-mel