This is a rough guide for M16 magazines, more aimed at gaming...
1964 - Original "waffle" 20-round.
1965 - Alloy follower 20-round. NSN 1005-00-056-2237
1972 - Black plastic follower 20-round. Same NSN.
1967 - Original Colt 30-round, dark-green follower.
1972 - Black follower 30-round. NSN 1005-00-921-5004.
1992 - Green follower 30-round. Same NSN.
2004 - Magpul Gen I Self-Leveling Follower (coyote tan).
2006 - Magpul Gen II Self-Leveling Follower (gray or orange).
2008 - Magpul Gen III Self-Leveling Follower (foliage green or yellow).
2009 - Tan follower 30-round. NSN 1005-00-561-7200.
2016 - Enhanced Performance Magazine, tan body with blue follower 30-round. NSN 1005-01-630-9508.
2007 - Magpul introduces the PMAG 30.
2009 - PMAG 30M or Rev M introduced.
2009 - EMAG introduced.
2013 - Rev M rebranded as PMAG 30 Gen M2 MOE.
2013 - PMAG 30 Gen M3 introduced, merges PMAG and EMAG lines.
Some PMAGs have NSN's (depending on generation and color) but aren't actually adopted until the USMC standardizes the Gen M3 windowed magazine in Medium Coyote Tan with NSN 1005-01-659-7086 in late 2016 / early 2017.
1983 - Thermold 30-round for Canada.
1982 - Orlite 30-round introduced.
1992 - Orlite 30-round with metal feed lip reinforcement.