I've taught myself:
-how to use a drysuit - me and my buddy bought them and then jumped straight in with them. I am generally slow to pick up dive skills but I took to drysuit diving like a natural so I figure it must be easy to learn
-navigation - I did do the SSI Nav class but learned nothing much so have learned more since then
-different types of gear (i.e. doubles, pony, BP/W) - had a bit of help from friends who've loaned me gear to try out
-photography - though I have gotten tips here and there from different people
-marine life ID - just bought a bunch of books and now I can ID most local critters
-correct weighting - read about it on the net
-gas management - internet again, and then in my nitrox class my instructor confirmed what I learned online
-nitrox - learned off the internet to help my buddy with his class though I did a class myself afterwards to have the card to get fills
-different kicking styles like frog kick, helicopter turns and back kick (still suck a bit at back kicks) - saw youtube videos and copied them. My buddy also filmed me so I could see what I looked like and so I knew what to fix.
-correct trim and buoyancy - this was related to fixing my weighting and both happened around the same time
-solo diving - I just started diving by myself one day to see what it was like and loved it!
-how to perform a bunch of skills midwater - such as mask clearing + removal/replacement, buddy breathing maskless, shooting an SMB, etc etc - in all my other classes we did them kneeling on the bottom
-drift diving - quite early on I got stuck in a boat that missed slack so I did my first drift dive with a few brief instructions from my buddy. I did do a drift class after this though (useless) as part of my AOW.
I am not against classes at all, just over time I've started to pick up stuff on my own or with a bit of help from more experienced divers.