Youlean Loudness Meter - Free VST, AU and AAX plugin
Amazon.com: Pyle Digital Handheld Sound Level Meter - Meter Automatic with A and C Frequency Weighting for Musicians and Sound Audio Professionals, 9V Battery Type - Pyle SPL25, Red/Black (PSPL25) : Industrial
Blue Cat's DP Meter Pro - Peak, RMS, Crest factor and Dynamic Range Monitoring, with MIDI CC or Automation Generation