I'm looking into Snort to carry our basic intrusion detection, but finding it hard going. What other Intrusion Detection software is there that is good to use for SQL Server?
You should look not into IDS technologies but Database Activity Monitoring (& Prevention). DAM(P) software shims itself in to watch all SQL queries and results and uses a combination of generic rules and guided knowledge to detect and in some cases prevent inappropriate use.
An IDS will catch SQL injection, which is more specifically aimed at web applications (and impacts databases as an end-state). It generally won't have any rules specific to normal database operations.