Monitoring Recommendations (NOC?)

We have a growing network, especially the remote portion of it. We rent racks at a remote datacenter where we have a few virtual environments (vSphere) set up and we'd like to closely and monitor those environments when these projects go completely live. Even at our headquarters, we're growing a tad bit and recently got hit with something and had to go searching for the cause, so we'd like to possibly implement something here as well. It was the internal monitoring of the software for that device that allowed us to track the issue and stifle it, and we do have logs but we'd like to have perhaps a central monitoring system (with a one-screen overview) where we can monitor everything or as much that's relevant as possible (our primary concern is the remote datacenter, since much more traffic will be expected there, but if affordable, we'd like one for here too, or, one integrated system for everything). Hardware, performance, security, alerts, etc. - is there a decent NOC or NOC-like system/software used for this? This area is new to me (and us) and we're a pretty small biz so please recommend a starting point that can get us going on this that wouldn't be overkill and is straightforward. Thanks.