Find Music Note from Frequency (Hz) - Online Calculator
This calculator will give you the nearest note to a given frequency as well as it's MIDI number - useful perhaps for when you want to find a "problem" note within your mix to target.
Notes and their Frequencies
Find Note from Frequency Calculator
This 'note-from-frequency' calculator will help you find the nearest note (note-name and midi-number) from a frequency.
For example: 440 hz = A4
You might also find this useful to correct a slightly out-of-tune vocal or instrument within your mix if you're using, for example; Antares AutoTune or the pitch-shifter in Sonic Foundry's SoundForge, or whatever.