Somethings I remember generating a lot of excitement at first.
Mining, when it could still be done with graphics cards and early mining machines.
Gambling, the early sites SatoshiDice and later Just-Dice had huge followings.  Looks like there is still a lot of crypto gambling just split up over many more sites now.
The early Altcoins such as Dogecoin and Huntercoin.
Tokens and Dapps made possible with Ethereum.
Earlier Tokens with the airdrops were very profitable.
Dapps looked very promising at first, not sure they've lived up to it yet.

What do you think is next?