SQL Server Monitoring Tools
I've voted to close this, because it's essentially a poll question, and there isn't a possible "right answer." You should be evaluating the vendors' offerings to see which product best suits your requirements and budget. Nobody can tell you which product will do that best.

The major vendors you want to investigate are:


SQL Sentry
Quest FogLight / SpotLight
Confio Ignite
RedGate SQL Monitor
Microsoft System Center Operations Manager
Idera Diagnostic Manager


They all have evaluation versions so you can test them out. In addition to feature sets you'll want to baseline your workloads and check the additional overhead each monitoring solution adds - no monitoring is 100% free.