For a normal (not performance/stress testing) you would be OK with the following:
- Request Bytes Out Total (very important especially for web (not intranet) applications)
- Requests Failed
- Requests/Sec
- Errors During Execution
- Errors Unhandled During Execution
- Session SQL Server Connections Total
- State Server Sessions Active
For the performance testing you would probably want things like:
- % CPU Utilization (make sure you're checking for very low CPU utilisation as well as it might indicate that something is dead)
- Requests Queued
- Output Cache Hits
