Looking for a Small Business Network Monitoring solution

This is my 1st question on this site, so looking forward to some of the responses. I'm looking for something that can monitor and notify on resource availability, and resource performance (mainly disk space, CPU, memory). We're an R&D company and have approx 40-50 VMs that we'd like to monitor. In addition we have about 8 x 24 port SMB Cisco switches, I'd also like to use it to monitor our CISCO ASA 5525. In the past the Netflow monitor has come in handy to trace some questionable communications, and monitor bandwidth activity.

Thanks in advance for any feedback

Mike