Hi,
An obvious choice (if you have the licensing) would be to use vRealize Operations Manager from VMware. This plugs into your vCenter and is able to offer a multitude of alerting and configuration which is highly customizable. The benefit is that this is built by VMware for VMware products and can give you some excellent insight into your environment.
If you are looking for something third party, then I have worked for organisations that use Icinga/Nagios and Solarwinds. Both worked well and can be good if you are trying to use one tool to monitor absolutely everything, especially if you are trying to manage a large heterogeneous infrastructure. With all monitoring products, it is about putting in the time to get everything right for your organization: alerts, emails, thresholds, etc. It is a work in progress but the benefits can be reaped if the time is put to configure them properly.