Bob's Pick...
MEILI SM5010: I use mine for finding and identifying unknown signals (it has audio output!), optimizing antennas, and as a spectrum display unit with my wide-coverage receiver. This is the most cost-effective instrument available.
 

The SM5010 spectrum analyzer is indispensable for viewing an entire block of radio spectrum, revealing unknown signals. Choose small segments under 1 MHz wide, or step sequentially up to a giant swath of more than 1 GHz , observing all signals in the spectrum.

Bob's Pick...
MASTECH multimeter: This meter continues to amaze me with its enormous number of useful functions. Even Judy uses it for environmental control growing orchids!

Nothing comes close to the multiple functions of the MS8209 with its “5 in 1” concept to measure sound level, light intensity, humidity, temperature, and electrical measurements including AC and DC volts, current, resistance, frequency and capacitance.

The WiNRADiO ERD-1500 Electromagnetic Radiation Detector is an exceptionally efficient "RF Sniffer" developed to quickly and reliably locate sources of electromagnetic interference. The detector contains a miniature wide-band antenna with a quality amplifier and high-performance Schottky barrier detection diodes for maximum sensitivity.

The shirt-pocket MFJ-886 offers 1 MHz-3 GHz frequency range, a 100 MHz sensitivity of 0.8 mV and readout to 1 Hz, all from a large (3/4"H), 10-digit LCD!

HF/VHF/UHF Antenna/SWR Analyzer With built-in 170 MHz frequency counter!

The ZC-185 is a quality instrument that detects and displays RF (Radio Frequency) signal levels with uniquely high sensitivity, similar to a broadband receiver. It provides Linear and Logarithmic measurements of RF signals over a broad span of frequencies. The ZC-185 allows the user to detect and measure signal strength and to distinguish between analog and digital transmissions.