from Microsoft is also pretty good. The SQL management packs were quite good. The benefit is that its Microsoft, the management packs are (were) written by the SQL team and the SCOM can be used monitor more than just SQL (Exchange, OS, etc, etc). SCOM uses an agent on the server, so you can monitor and see how much of an impact the agent has on the server.
I used Idera at a previous place, and did not like it. It uses an agentless method and "pulls" information from the server. This can compound issues when a server is performing poorly.