Abyssal Whip - From 3,75M when I was killing abyssal demons to a mere 100K... Just lost my main source of income.
Red Chinchompa - From 600-700 GP to 60 GP... Just lost my motivation to get from 91 hunting to 99.
Godswords - From 25M+ to a mere 7-8M... God Wars now appear to be useless.
Amulet of Fury - From 20M to 3M... I just lost about 17M there (although I bought it for maybe 1,75M )
Dragon Claws - Dozens of millions to a few hundred K's...
Dragonfire Shield - Dozens of millions to a million or so (basically made metal dragons useless)
If I understand correctly, it is both the result of the return of the wilderness and free trade (botting, less items being taken out of the game - mainly why the whip is worthless), the new combat systems (new items, new ways to train - why the chins are worthless, no special attacks), etc?
Whips - The price is low because killing them is so quick, theres been a lot that came into the game and with new weapons they aren't as desirable
Red chins - They crashed with EoC because they were made useless plus bots didn't help at all, check the highscores on hunter there's so many 200m xp red chin bots
Godswords - Similar reason to whip
Fury - The fight kiln introduced a onyx farming method so that contributed to lowering the price more
D claws - EoC made them useless due to loosing their unique spec
DFS - Probably since most metal dragons with the exception of miths, you can camp them easily. (Bone crusher with demon horn neck = unlimited prayer) Also bots
Now days the best money making methods are through high level content such as PvM (Nex, kalphite king) and gano beasts are good among other things