I use EAS Inspector. It has loads of features, and it tells you how much headroom you have.
Technical
Spectrum analyzer
Customizable alarms for:
- Headroom
- Channel balance
- Number of times audio waveform is clipped
- Number of consecutive samples clipped
- Total number of clipped samples
Peak meters
RMS meters
Channel balance meter
Customizable meter caution and warning zones
Headroom displays/readouts
Clip counters/readouts
Supports sampling rates up to 192 kHz
Altivec/Velocity engine optimizations
Multi-processor/Advanced multi-processor (AMP) capable
Interface

Enable/disable spectrum analyzer
Enable/disable individual alarms
Set individual alarm levels using arrow controls
General

Integrated SAVE and LOAD

and it`s a FREE!!!! Vst plugin

http://www.elementalaudio.com/produc...oad/index.html