I found this at www.offshorestrategies.com and thought it was useful enough to copy here. Good thing too, it's gone from there now!

Here's another reference just for locking plugs/recepticals:
https://www.stayonline.com/product-resources/nema-locking-reference-chart.asp

These are the outlets, not the plugs.

NEMA No.	Config	Rating
L5-15		15A, 125V 2P, 3W
L5-15  5-15		15A, 125V 2P, 3W
L6-15		15A, 250V 2P, 3W
L7-15		15A, 277VAC 2P, 3W
L5-20		20A, 125V 2P, 3W
L6-20		20A, 250V 2P, 3W
L7-20		20A, 277VAC 2P, 3W
L8-20		20A, 480VAC 2P, 3W
L5-30		30A, 125V 2P, 3W
L6-30		30A, 250V 2P, 3W
L7-30		30A, 277VAC 2P, 3W
L8-30		30A, 480VAC 2P, 3W
L14-20		20A, 125/250V 3P, 4W
L15-20		20A, 250V 3Ø 3P, 4W
L16-20		20A, 480V 3Ø 3P, 4W
L14-30		30A, 125/250V 3P, 4W
L15-30		30A, 250V 3Ø 3P, 4W
L16-30		30A, 480V 3Ø 3P, 4W
L21-20		20A, 120/ 208V 3/Y 4P, 5W
L22-20		20A, 277/ 480V 3/Y 4P, 5W
L23-20		20A, 347/ 600V 3/Y 4P, 5W
L21-30		30A, 120/ 208V 3/Y 4P, 5W
L22-30		30A, 277/ 480V 3/Y 4P, 5W
L23-30		30A, 347/ 600V 3/Y 4P, 5W

NEMA No.	Config	Rating
1-15		15A, 125V 2P, 2W
5-15		15A, 125V 2P, 3W
5-20		20A, 125V 2P, 3W
5-30		30A, 125V 2P, 3W
5-50		50A, 125V 2P, 3W
6-15		15A, 250V 2P, 3W
6-20		20A, 250V 2P, 3W
6-30		30A, 250V 2P, 3W
6-50		50A, 250V 2P, 3W
14-30		30A, 125/250V 3P, 4W
14-50		50A, 125/250V 3P, 4W
14-60		60A, 125/250V 3P, 4W

IEC plugs and recepticals

IEC number	Config.	rating (amps)
C1 & C2		0.2
C3 & C4		2.5
C5		2.5
C5 & C6		2.5
C7 & C8 (C8 not shown)		2.5
C7 polarized		2.5
C9 & C10		6
C11 & C12		10
C13		10/15
C14		10/15
C15		10/15
C15 & C16		10/15
C15-a & C16-a		10/15
C17 & C18		10/15
C19		16/20
C20		16/20
C21 & C22		16/20
C23 & C24		16/20